ActorMenu: Changed API to be able to build a GMenuModel.

This is better than playing with the XML code in the frontend.
Call History: Adapted to new ActorMenu API.
Main Window: Adapted to new ActorMenu API.
Call Core: Made code easier to read.
H323: Fixed compilation warning.
Call Core: Fixed call & transfer actions validity check.

We should only be able to call when there is no active call.
We should only be able to transfer when there is one active call.
Roster: Fixed roster with dark theme.

Never hardcode colors.