convert App to subclass of dict to support parsing/dumping libs

Python is heavily based on its core data types, and dict is one of the more
important ones.  Even classes are basically a wrapper around a dict. This
converts metadata.App to be a subclass of dict so it can behave like a dict
when being dumped and loaded.  This makes its drastically easier to use
different data formats for build metadata and for sending data to the
client.  This approach will ultimately mean we no longer have to maintain
custom parsing and dumping code.

This also means then that the YAML/JSON field names will not have spaces in
them, and they will match exactly what it used as the dict keys once the
data is parsed, as well as matching exactly the instance attribute names:

* CurrentVersion: 1.2.6
* app['CurrentVersion'] == '1.2.6'
* app.CurrentVersion == '1.2.6'

Inspired by:
https://goodcode.io/articles/python-dict-object/

tests/metadata/dump/org.adaway.yaml

@@ -1,17 +1,17 @@
 AntiFeatures: []
-Archive Policy: null
-Author Email: null
-Author Name: null
-Auto Name: AdAway
-Auto Update Mode: Version v%v
+ArchivePolicy: null
+AuthorEmail: null
+AuthorName: null
+AutoName: AdAway
+AutoUpdateMode: Version v%v
 Binaries: null
 Bitcoin: null
 Categories:
 - System
 - Security
 Changelog: ''
-Current Version: '3.0'
-Current Version Code: '52'
+CurrentVersion: '3.0'
+CurrentVersionCode: '52'
 Description: 'An ad blocker that uses the hosts file. The hosts file
 
   contains a list of mappings between hostnames and IP addresses. When
@@ -38,24 +38,24 @@ Description: 'An ad blocker that uses the hosts file. The hosts file
 Disabled: null
 Donate: http://sufficientlysecure.org/index.php/adaway
 FlattrID: '369138'
-Issue Tracker: https://github.com/dschuermann/ad-away/issues
+IssueTracker: https://github.com/dschuermann/ad-away/issues
 License: GPLv3
 Litecoin: null
-Maintainer Notes: ''
+MaintainerNotes: ''
 Name: null
-No Source Since: ''
+NoSourceSince: ''
 Provides: org.sufficientlysecure.adaway
 Repo: https://github.com/dschuermann/ad-away.git
-Repo Type: git
-Requires Root: true
-Source Code: https://github.com/dschuermann/ad-away
+RepoType: git
+RequiresRoot: true
+SourceCode: https://github.com/dschuermann/ad-away
 Summary: Block advertisements
-Update Check Data: null
-Update Check Ignore: null
-Update Check Mode: Tags
-Update Check Name: null
-Vercode Operation: null
-Web Site: http://sufficientlysecure.org/index.php/adaway
+UpdateCheckData: null
+UpdateCheckIgnore: null
+UpdateCheckMode: Tags
+UpdateCheckName: null
+VercodeOperation: null
+WebSite: http://sufficientlysecure.org/index.php/adaway
 added: null
 builds:
 - antcommands: []

tests/metadata/dump/org.smssecure.smssecure.yaml

@@ -1,16 +1,16 @@
 AntiFeatures: []
-Archive Policy: null
-Author Email: null
-Author Name: null
-Auto Name: SMSSecure
-Auto Update Mode: Version v%v
+ArchivePolicy: null
+AuthorEmail: null
+AuthorName: null
+AutoName: SMSSecure
+AutoUpdateMode: Version v%v
 Binaries: null
 Bitcoin: null
 Categories:
 - Phone & SMS
 Changelog: ''
-Current Version: 0.6.0
-Current Version Code: '102'
+CurrentVersion: 0.6.0
+CurrentVersionCode: '102'
 Description: 'SMSSecure is an SMS/MMS application that allows you to protect your
   privacy while communicating with friends.
 
@@ -35,24 +35,24 @@ Description: 'SMSSecure is an SMS/MMS application that allows you to protect you
 Disabled: null
 Donate: null
 FlattrID: null
-Issue Tracker: https://github.com/SMSSecure/SMSSecure/issues
+IssueTracker: https://github.com/SMSSecure/SMSSecure/issues
 License: GPLv3
 Litecoin: null
-Maintainer Notes: ''
+MaintainerNotes: ''
 Name: null
-No Source Since: ''
+NoSourceSince: ''
 Provides: null
 Repo: https://github.com/SMSSecure/SMSSecure
-Repo Type: git
-Requires Root: false
-Source Code: https://github.com/SMSSecure/SMSSecure
+RepoType: git
+RequiresRoot: false
+SourceCode: https://github.com/SMSSecure/SMSSecure
 Summary: Send encrypted text messages (SMS)
-Update Check Data: null
-Update Check Ignore: null
-Update Check Mode: Tags
-Update Check Name: null
-Vercode Operation: null
-Web Site: http://www.smssecure.org
+UpdateCheckData: null
+UpdateCheckIgnore: null
+UpdateCheckMode: Tags
+UpdateCheckName: null
+VercodeOperation: null
+WebSite: http://www.smssecure.org
 added: null
 builds:
 - antcommands: []

tests/metadata/dump/org.videolan.vlc.yaml

@@ -1,16 +1,16 @@
 AntiFeatures: []
-Archive Policy: 9 versions
-Author Email: null
-Author Name: null
-Auto Name: VLC
-Auto Update Mode: None
+ArchivePolicy: 9 versions
+AuthorEmail: null
+AuthorName: null
+AutoName: VLC
+AutoUpdateMode: None
 Binaries: null
 Bitcoin: null
 Categories:
 - Multimedia
 Changelog: ''
-Current Version: 1.2.6
-Current Version Code: '1030005'
+CurrentVersion: 1.2.6
+CurrentVersionCode: '1030005'
 Description: 'Video and audio player that supports a wide range of formats,
 
   for both local and remote playback.
@@ -22,10 +22,10 @@ Description: 'Video and audio player that supports a wide range of formats,
 Disabled: null
 Donate: http://www.videolan.org/contribute.html#money
 FlattrID: null
-Issue Tracker: http://www.videolan.org/support/index.html#bugs
+IssueTracker: http://www.videolan.org/support/index.html#bugs
 License: GPLv3
 Litecoin: null
-Maintainer Notes: 'Instructions and dependencies here: http://wiki.videolan.org/AndroidCompile
+MaintainerNotes: 'Instructions and dependencies here: http://wiki.videolan.org/AndroidCompile
 
   see http://buildbot.videolan.org/builders/ for version code scheme
 
@@ -42,19 +42,19 @@ Maintainer Notes: 'Instructions and dependencies here: http://wiki.videolan.org/
 
   '
 Name: null
-No Source Since: ''
+NoSourceSince: ''
 Provides: null
 Repo: git://git.videolan.org/vlc-ports/android.git
-Repo Type: git
-Requires Root: false
-Source Code: http://git.videolan.org/?p=vlc-ports/android.git;a=summary
+RepoType: git
+RequiresRoot: false
+SourceCode: http://git.videolan.org/?p=vlc-ports/android.git;a=summary
 Summary: Media player
-Update Check Data: null
-Update Check Ignore: null
-Update Check Mode: Tags
-Update Check Name: null
-Vercode Operation: '%c + 5'
-Web Site: http://www.videolan.org/vlc/download-android.html
+UpdateCheckData: null
+UpdateCheckIgnore: null
+UpdateCheckMode: Tags
+UpdateCheckName: null
+VercodeOperation: '%c + 5'
+WebSite: http://www.videolan.org/vlc/download-android.html
 added: null
 builds:
 - antcommands: []