[KPhotoAlbum] mark untagged menu item patch

[Tobias Leupold]

I added your patch with slight modifications (cf. e8c2b41 and fcd7ddc). I 
think not having the "untagged image" tag in the annotation dialog and adding 
a "mark as untagged" action as you proposed is a really nicer way to handle 
this than some annotation dialog "hack" ;-)

Thanks again for the patch! perhaps, you also want to join #kphotoalbum on 
freenode from time to time?