[REVIEW ONLY] Split View Refactoring

This is the refactoring effort to move Working Set API's and start deprecating some of the DocumentManager APIs

This probably isn't ready for prime time consumption but want to get any feedback on the approach and if there is anything I forgot. 

Also I encourage as much test exposure as possible to make sure nothing is broken.
Not sure how you are expecting `@param` to render in the middle of description, but this whole "render" bullet gets rendered inline. May want nested bullets:

```
     *      - @param {!string} fullPath Path to the image file
     *      - @param {!jQueryObject} $editorHolder The DOM element to append the view to.     ```