add a special Provides: to all login manager packages

[Kevin Kofler]

Colin Walters wrote:
> ramifications for the layers involved.  Instead, it should be focused
> on a product or goal - desktop and server images being good choices.

Just one desktop image?! You can pry our KDE image from my cold, dead hands!

And FWIW I'm sure the XFCE and LXDE maintainers also think similarly, even
though their spins are already treated as second-class citizens (torrent
only, and only on spins.fp.o rather than torrent.fp.o).

        Kevin Kofler