Qt: Add the colorization action.

Change-Id: I846a48c35c4ef3bbbcf17d03885acc5be8c9a6b5
Reviewed-on: https://code.wireshark.org/review/4259
Petri-Dish: Gerald Combs <gerald@wireshark.org>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Gerald Combs <gerald@wireshark.org>