View, edit and enforce project settings.

Thanks for writing this package! Fits my use case nicely.

This pull request builds off the existing edit settings command, adding a user interface for editing existing projects.

It includes the ability to add project-specific configuration options that override default and user defaults!

(Sorry there are no specs.. I didn't see too many and I'm just getting the hang of atom package development.)

Here's a screenshot of the 'Edit Projects' page:

![screen shot 2014-08-19 at 11 51 22 pm](https://cloud.githubusercontent.com/assets/588040/3977456/3a6dcb2c-2839-11e4-8023-0d69e7b41b25.png)