add garbage collection

[InstinctBrett]

commands, eventsheets, tokenslots and tokens are not being deregistered correctly when destroyed. A container is not telling its contents to destroy correctly. This could cause memory leaks if the robot editor was used for extended periods of time.

objects need to:

• remove their node from the dom document
• not hold onto their node reference
• unregister from all events they were listening to

helpful thoughts: http://docstore.mik.ua/orelly/webprog/jscript/ch11_03.htm