Implement History Functionality as per spec and treatments.

Please assess then implement the History Tab in the CB as per the specification here:

http://docs.google.com/a/curriki.org/Doc?docid=dhksk8r2_1dd5m6c&hl=en_US

and in accordance with the design treatments here:

http://www.curriki.org/xwiki/bin/view/Project/History