#2 Remove empty database entires in pull down menues

[Anonymous]

I had a few mis-typed artists. After renaming the
artists and re-run a "Scan Collection" in amarok, the
old (mis-typed) artists still exist in the database.

Amarok really should clear these entries, but also the
web frontend should not display any entries with a
count = 0

Also: Old genres, albums, ... are kept in the database
but should be removed from the web-forntend display