Move Montage bindings methods into core/bindings
Move path methods from Object.prototype to Montage

And add observePath, observeKey, and observeProperty.

Paths can be observed on non-Montage objects using generic calls.

    Montage.observePath.call(object, …)
ContentController.avoidsEmptySelection
Shuffle Montage.didCreate around
Add repetition iteration isFirst/isLast