New fork icon!

## What does this MR do?
We are using the old fork icon for branching only, so this implements our new custom fork icon

## Screenshots (if relevant)
![Screen_Shot_2016-07-15_at_9.22.33_AM](/uploads/05abaffff314e41f582189327bcca6b2/Screen_Shot_2016-07-15_at_9.22.33_AM.png)     
![Screen_Shot_2016-07-15_at_9.29.14_AM](/uploads/a08c622c92da00945406bbd4b3497749/Screen_Shot_2016-07-15_at_9.29.14_AM.png)

cc @hazelyang 

See merge request !5276