[KPhotoAlbum] Assigning tags to groups

[Tobias Leupold]

> 2) More seriously, if you assign a tag to a group, and that tag is
> already under another group, that relationship is not removed,
> breaking the hierarchical relationship.

I think it's intended that a tag can't only be member of one group, but of
multiple ones. E. g. "Esbjerg" can be part of "Denmark" as well as of "Party
Locations".

IIRC, the original relationship display was groups on the left and members on
the right side, and each tag could/can be a member of each group. I thought a
tree view was better, as nested groups were possible but the display could not
show them. And thus, I wrote an algorithm translating the parent-child
relatinship to a tree view.

That was quite some time ago, so I'm not sure if I implemented it correctly
back then (but I hope so!). But imo, definitely, it must be possible for a tag
to be member of multiple groups.