Allow CLAs to be updated

:fork_and_knife: This adds the ability to update CLA signatures. It also starts to move in the direction of the CLA mockups where the signature form is in the left column and the CLA is in the right column.

This is what it looks like now.

![screen shot 2014-02-03 at 3 44 32 pm](https://f.cloud.github.com/assets/316507/2069426/8c657602-8d14-11e3-8be0-330bdeb9fe53.png)