implement gettext localization

This allows all the text to be localized via Weblate.  This is a quick
overview of all the strings, but there are certainly some that were left
out.

closes #342

fdroidserver/__init__.py

@@ -0,0 +1,22 @@
+
+import gettext
+import glob
+import os
+import sys
+
+
+# support running straight from git and standard installs
+rootpaths = [
+    os.path.realpath(os.path.join(os.path.dirname(__file__), '..')),
+    sys.prefix + 'share',
+]
+
+localedir = None
+for rootpath in rootpaths:
+    if len(glob.glob(os.path.join(rootpath, 'locale', '*', 'LC_MESSAGES', 'fdroidserver.mo'))) > 0:
+        localedir = os.path.join(rootpath, 'locale')
+        break
+
+gettext.bindtextdomain('fdroidserver', localedir)
+gettext.textdomain('fdroidserver')
+_ = gettext.gettext