Add ability to relaunch

Adds a menubar item to relaunch Amethyst.

We could also add a hotkey people think that would be useful

Addresses https://github.com/ianyh/Amethyst/issues/94

Also effectively addresses https://github.com/ianyh/Amethyst/issues/79
Picture
![screen shot 2013-11-22 at 6 56 57 pm](https://f.cloud.github.com/assets/3766436/1605755/f6536a32-53ea-11e3-9867-74e15ed0b509.png)