Improve selects for files table by removing the (f.album <> '' AND
f.album IS NOT NULL) from the where clause for album and artist. These
are unnecessary because forked-daapd makes sure that an artist or album
name exists.
Improve select for files table by removing f.media_kind = 32 from the
queries (forked_daapd has no media_kind = 32).
Optimize the indexes on the files table to speed up select queries