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TNL-291

@andy-armstrong @cahrens please review.

@talbs thanks for the front-end work :smile: 

@explorerleslie would you like me to create a sandbox?
I like how you've refactored the method to pass most of the complexity via the options. Given that, it seems that overriding ```createChildView``` itself isn't really necessary anymore. Instead you could have two methods that you can optionally override:
1. ```getChildViewClass``` - returns the class of child to make
2. ```getChildViewOptions``` - returns the options to pass to each child

My gut is that this would make it easier to override than having to remember to call the prototype's method.