Only overwrite the app URL if the AppStream URL exists
gnome-weather has upstream data, remove our copy
Fix BuildPkg without extract-package
Don't extract .desktop files from common packages

desktop files should always be shipped in the primary application
package, and this way we remove the duplicate scummvm entries.
Add support for translations

When multiple languages are available in one appdata or desktop file,
instead of merging everything togheter, add multiple name/summary/
description tags with different xml:lang attributes.
To do so, we also need to switch from ConfigParser to GLib.KeyFile,
which also implies switching to the introspected bindings for
GdkPixbuf and Rsvg.
Implement translations for appstream data too

Read and parse the xml:lang variant of the support markup
for <description>, to create localized pre-formatted descriptions
that are then merged into the final appstream file.