Add options to enable/disable specific services
More and more external services were or will be added to the app which also increases the number of API requests and data volume. If someone will save bandwith and just want to use the main features it would make sense to add options to enable or disable a specific service.
- last.fm Scrobble (already available as option)
- last.fm metadata
- MusicBrainz metadata
- Wikipedia article (to be implemented - see issue #27)