Allow users to add their own Android apps to their local profile/GDG

[friedger]

This issue is about the UI on frisbee, not the server code on the GDG-x hub.

The app should provide an intent filter for sharing android apps. The package name of shared apps are stored as preference in the app (and later uploaded to the GDG-x hub.

The preferences show a list of registered apps and allow to remove an app, to mark an app as public