Add board fork functionality. Fixes #65

![screen shot 2014-08-07 at 6 08 27 pm](https://cloud.githubusercontent.com/assets/1996521/3851597/928168fa-1e98-11e4-9984-4ba8c8463cd3.png)

do we have to delete any dom-specific stuff from the board data?  like remove the ephemeral stuff?