Don't use IndexerAdapter when not sorting alphabetically in AlbumsFragment

also #671
make Album sorting choices a ListPreference

let user choose between alphabetically, album year and last modified
for #671
Tell MusicBuilder about MPD's "directory" keyword

The info MPD has given for a "directory" was added to the "file"
in the list before.
This fix is needed for #671 because directories have Last-Modified
Bit of a hack because Tools.getRanges is hardly curable.
Simplify uniqueness-mechanism in search results
Make search look for both Artist and AlbumArtist

fixes #673