Code Review: Kitten and Location Representations

[marlitas]

A review for both the model and view classes that create the Kitten and Location-based representations would be helpful, and I believe was not part of the review in #20

Please feel free to close this issue if that is incorrect.

Classes that should be a part of this review:

• KittenNode
• KittensLayerNode
• LocationCountingObjectNode
• LocationCountingObjectsLayerNode
• TenFrameButton
• CommutativeButton

Additionally, logic was added to the following files due to the implementation of the above:

• CountingObject
• NumberPairsModel
• NumberPairsScreenView