use common method to set up defaults in metadata dict
use common method to set up defaults in metadata dict

This is needed for the upcoming metadata formats: JSON, XML, etc.

f-droid/fdroid-server,f-droid/fdroid-server,fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroid-server,f-droid/fdroidserver