CLA invitation, signing and support screens (sign in, sign up, invite accept/decline)

:fork_and_knife:  Adds styling and clean up for ICLA/CCLA invitation process and related screens.

##### Sign ICLA
![image](https://f.cloud.github.com/assets/438082/2154319/20a07310-9433-11e3-92bf-cd6880d2aaef.png)

##### Sign CCLA
![image](https://f.cloud.github.com/assets/438082/2154324/3181b806-9433-11e3-8e4c-79e1d2bf3652.png)

##### Invite CCLA Contributor
![image](https://f.cloud.github.com/assets/438082/2154297/e372c98e-9432-11e3-91db-1ac7c8ffd493.png)

##### Accept/Decline CCLA Contributor Invitation
A note here: [In the wireframe flow](https://layervault.com/rev/PtfOTFfmOe), we'd like to allow user to accept or decline straight from the invitation email. The Accept or Decline buttons in the email, respectively, would drive user to the correct step in the process based on conditions outlined in the wireframe. I don't know if we're making this change at this time.
![image](https://f.cloud.github.com/assets/438082/2154356/9d0f0a1a-9433-11e3-81d1-94103c70304f.png)

##### Sign In/ Create Account
![image](https://f.cloud.github.com/assets/438082/2154337/54c4d2a8-9433-11e3-93ca-087d0d6b8375.png)

![image](https://f.cloud.github.com/assets/438082/2154338/59cbf70e-9433-11e3-9fbd-22f122d23ff0.png)