Ensure that all view observers are scheduled

Previously Ember.View#registerObserver did not schedule observers as part of
the 'render' queue. In some cases we implemented an additional 'invoker'
that took care of this but it was not universally applied. Here we move the
scheduling into registerObserver itself. This will help prevent unnecessary
DOM updates.
Merge pull request #2307 from CrowdStrike/scheduled-view-updates

Ensure that all view observers are scheduled