New extension loading

This is still very WIP, but we have

- configure multiple branches
- pick which "runner" to use
- enable & drag & drop reordering of plugins
- provider agnostic

You can grab this and go to "/test/project_config" to play with the goodness.

The UI has not been fully hooked up to the backend yet -- still need to make sure old db documents are automatically updated.

![screen shot 2013-09-12 at 11 56 34 pm](https://f.cloud.github.com/assets/112170/1136262/2459b1ae-1c3a-11e3-9e9a-472a37e96295.png)