import app into fdroid directly from git clone

This adds a new method for `fdroid import` that will generate the fdroidserver
metadata based on a local git repo.  This new mode generates the metadata in
the new .fdroid.yaml format in the git repo itself.  It is intended as a quick
way to get starting building apps using the fdroidserver tools.

setup.py

@@ -27,6 +27,7 @@ setup(name='fdroidserver',
                   'examples/fdroid-icon.png']),
       ],
       install_requires=[
+          'GitPython',
           'mwclient',
           'paramiko',
           'Pillow',