[KPhotoAlbum] Super categories makeover

[Tobias Leupold]

Hi List/Johannes!

Would you/someone be so kind to have a look at the current supercategories 
branch? I think most of the functionality is implemented now. Groups can be 
added, renamed and deleted. When a group is selected as a member of another 
group, the tree view is updated accordingly.

I also fixed a bug in FileReader: when adding a new group but no members are 
selected, the group was written to the db, but it was not added to the 
memberMap on a later reload. Now, empty groups show up again.

Apart from the fact that the new code surely needs some review, I'm a bit 
stuck at the drag-and-drop thing now. What it should and should not do is 
quite obvious: a group must not be dragged to another category or to the top 
level. When it's dropped, the user should be asked (by a context menu) if the 
group should be copied there (become a new member of the target group) or 
moved there.

I found out how to enable drag and drop, but I don't really know how to do the 
rest at the moment ... all help would be greatly appreciated!

Yours, Tobias