Multiuser whiteboard control

I've added the ability for multiple users to write on the whiteboard at once. The way you control it is through an attribute in the WhiteboardModule section of config.xml.

You can add a parameter called "whiteboardAccess" and give it either a value of "presenter", "moderator", or "all".

presenter:  this is the same as it is now, only the presenter can access to the toolbar
moderator: this gives access to the presenter and also to moderators
all:            this gives access to everyone

The only real downside to my approach is that when you press the undo button the last element added is removed no matter who wrote it. I'm not sure that the development effort required to remember what user made what edit and have undo be user specific is worth it.