[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.
@redmunds Hmm, that seems like a problem.  This style of indentation is very common in our codebase when `@param` blocks run > 1 line... maybe we should file this as an apify bug before trying to reformat too much of our code.