gear menu

Adds a gear menu, implementing <https://trello.com/c/rgMas5C0/322-1-as-a-user-i-can-see-additional-actions-for-my-conversation-in-a-gear-window>.

At review/merge time, this will be hidden, as there is not yet anything to pick from the menu.  However, for the sake of seeing what the code does, some images:

![quietly awaiting attention](https://f.cloud.github.com/assets/425657/1604515/fe859dae-53bf-11e3-928d-cc71f013352e.png)
![dropped down](https://f.cloud.github.com/assets/425657/1604516/0180bb74-53c0-11e3-9918-055dd08a74d3.png)
![element selected](https://f.cloud.github.com/assets/425657/1604517/03a3916a-53c0-11e3-9dd5-524bb10e7fba.png)