Add a contact add/remove button in chat

For single chat sessions and those that are 'users' add a contact add/remove star to the chat menu next to call, upload file, and geolocation.

![chat-contact](https://cloud.githubusercontent.com/assets/4820641/5073732/6cbcc858-6e84-11e4-85ed-c30e812aac54.png)

Changed to `isUser`.