disable activation of the whiteboard

I'm proposing this is because of
- bug reports about assertion failures
- 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

https://gna.org/bugs/index.php?22231
https://gna.org/bugs/?func=detailitem&item_id=21302

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, and with sufficient unit tests to help prevent it from breaking in the future