Scope LayoutView regions to the view's elements

All right, this is a pretty busy PR and several others have already proposed alternates, however I think this is by far the cleanest way we can solve this issue.

Fixes #1685,  closes #2063, closes  #2033, and resolves #1951 

See those issues for more context, this solution was previously discussed in detail https://github.com/marionettejs/backbone.marionette/pull/2063#discussion_r21800528

/cc @jmca