Revisions: First pass an implementing a new UI/UX for reviewing the revisions of posts. See #23497 props adamsilverstein for the initial patch.

This implements a new revisions ui using Backbone and preserves all the old methods of "integration" so the change should be transparent to plugins using revisi
ons with CPTs.

This is the first pass and so there are a number of things still to be resolved, more details in the ticket. Feedback welcomed.
Merge revisions.css into wp-admin.css. Move misplaced block of revisions CSS in wp-admin.css into appropriate section. Some standards clean up and selector merging. see #23497.