adapters: Cleanup ArrayAdapter & ArrayIndexAdapter warnings.
Item: Fix a few potential null pointers.
SearchActivity: Small fixes.
SearchActivity: Fix a few potential NPEs.
views: Cleanup signatures.
NowPlayingFragment: Refactor track information intent sharing.
Album*DataBinder: Cleanup.
MainMenuActivity: Warning cleanup.
MainMenuActivity: onCreate() refactor.
MPD: Fix potential NPEs.
WeakLinkedList: Cleanup warnings.
MPDroidService: Wind down notification prior to stop on wind down.
Views: Cleanup.
MPDroid: Remove sortByTrackNumber, cleanup Music().compareTo().

This removes the sortByTrackNumber option due to developer consensus. This
fixes issue #546 by removing a potential general contract violation during
sorting. Thanks to @hurzl for the technical expertise and review of this code.