Refactor the weird picker god module into specific sub-impls in
playback and a new navigation package.
I cannot keep this unified. The needs are too different among each
picker. Better to keep it separate, especially in preparation for
the playlist dialogs.
Refactor the disjoint Library and Playlist setup into two new
DeviceLibrary and UserLibrary implementations.
This makes the API surface a bit less disjoint than prior.
Unify Indexer and MusicRepository into a single class.
This is meant to create a single dependency on PlaylistDatabase and
reduce the amount of orchestration.
Start injecting shared object instances.
This is not a 100% conversion, as certain portions of the code are not
really ready for 100% DI constructors just yet.
