Use new color_dissector_filters.[ch] to refactor (color) conversation generation in GTK menus.

Change-Id: I5868a40b71a989a3a1522cb091064bb0aaec6daf
Reviewed-on: https://code.wireshark.org/review/5828
Reviewed-by: Michael Mann <mmann78@netscape.net>
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>