disable activation of the whiteboard

I'm proposing this is because of
- outstanding bugs reporting assertion failures and similar that when without address for more than a year
- performance problems -- I tested both master and 1.12 branch and 1.11 series dating back to January
2014, and whiteboard moves no longer work fully, which was the most important part of the feature. It seems that the "future_map" which is supposed to control alternations of the gamestate from with planned moves / without planned moves is no longer working, so units with planned moves cannot be selected or moved properly.
- graphical glitches -- the "ghosted" unit standing animations are corrupted and twitch continuously while units with such animations have planned moves

I suggest that we might look towards restoring the whiteboard in version 1.14, if we can reimplement it in a more robust / maintainable manner