Workspace/WorkspaceView changes

This is a potential API for atom.workspace. The api's for Workspace and WorkspaceView are combined to create a single more approachable API.
But what about packages that don't have unified view/models like the image editor?

![screen shot 2014-07-22 at 9 36 13 am](https://cloud.githubusercontent.com/assets/671378/3661180/54a26fb6-11be-11e4-9e11-4cd41ff78cac.png)