[WIP] Make template context proxy.

This is a work in progress that would generate warnings if a view's properties were accessed without `view.` when `VIEW_PRESERVES_CONTEXT` is enabled (or set to 'warn').

The majority of tests pass at this point.  The remaining issue relates to views that define their own `contentBinding`.  

I plan to continue working on this, but figured it makes sense to get the code out there for a bit of a sanity check at this point.