Improve file deletion

[naveensingh]

Changes:

• Rescan paths when updating the local cache and when deleting files (so that we can create delete requests on R+).
• Avoid using @Delete and delete items one by one as it doesn't reflect the db changes immediately (thus UI isn't updated on time).
• Avoid calling notifyDatasetChanged() when displaying playlist tracks. Drag handles will still appear in action mode. I double-checked.
• Finish activity when all tracks are deleted as it doesn't make sense to show an artist/album without albums/tracks.
• Fix UI update glitch when deleting folder tracks.

[tibbi]

removed some extra ones ;) Thanks