Fixed a NPE in onUpgrade() mechanism introduced in rev 81d78cc3c95abe091ff029370ae15dc9076f7bc6. Improved documentation of AbstractApplication.
Refactored the release DAO, release service and release loaders.

Loaders are part of the GUI, they do not belong in DB package.

Clear separations of concerns: The service contains the business logic and can access other services. It delegates calls to the DAO. The GUI does never call the DAO directly. Its calls to the services are as simple as possible, because all logic is done in the services.

Introduced application wide constants for loader IDs.
Refactored DAO's method names in the style of spring data. Removed unused query.

Introduced implicit IsHidden =! true to all find...() method in release service.
Limited calls that show "all releases" ("available" and "all" tabs) to show only releases within the download release time period.
Refactored reloading of loader data when content changed.
The new solution is less object oriented but simpler and more reliable.
Updated referenced libraries
Opening MusicBrainz in internal WebView Activity instead of opening the
users browser
Implemented first version of info dialog in preferences, displaying version licenses and privacy policy