Fields revamp

This PR does two things:

A) Instead of a full-height modal with layer details, places data reference info inline to match data panel in style view:
![screen shot 2014-03-27 at 1 52 21 pm](https://cloud.githubusercontent.com/assets/108094/2540981/afd253ac-b5d8-11e3-8a7c-1e5998d7a494.png)

B) Adds context around fields form for local sources:
![screen shot 2014-03-27 at 1 51 44 pm](https://cloud.githubusercontent.com/assets/108094/2540991/d1e05732-b5d8-11e3-9d95-0a53601fefa5.png)