getting ready for 2.4: color and font pickers

[Matthias Clasen <maclas gmx de>]

I've just attached new versions of these to
http://bugzilla.gnome.org/show_bug.cgi?id=107682 and
http://bugzilla.gnome.org/show_bug.cgi?id=107597

Changes wrt to the previous versions:
- reduced some excessively long function names
- moved to instance private data
- improved documentation
- fixed a few bugs noticed while doing the above


I'm going to commit these in a few days, if nobody has further comments.


Matthias