Fix ui bindings for Collection and Composite Views

Fixes #1502.

Not going to lie, this was a bigger / more invasive change than I expected when I went in here.

This fixes a couple things that broke:
1. collectionView now invokes bindUIelements after rendering its children
2. compositeView now invokes bindUIelements after rendering its children

Interesting to note:
+ compositeView also invokes bindUIelements before rendering its children because childViewContainer could have ui interpolation


ha - oh yea. This *is* a new feature. This kinda explains that the whole thing is not a bug really, if it was never the intention to include ui elements for children. This would explain why collectionView, never bound the UI and compositeView bound it after the template. 

If we do this, we should probably revist Layout's and whether we want to introduce this behavior. My opinion at the moment is that we should do it because it's surprising when it doesn't work. With that said, I could be persuaded because: 1) accessing child elements is not best practice, 2) there could be a perf hit if the collection view has a huge $el. 

Share your thoughts @marionettejs/marionette-core