Determine default changeView behavior based on source order

Currently, the `changeView` method _requires_ a value for the `action` argument of either `"push"` or `"pop"`.

It would be nice if the source order of the views could determine the action to take in cases where that value is not provided. This could be accomplished by comparing the value of `@$views.index(@$activeView)` with the value of `@$views.index($targetView)`.

This could also allow us to add a new data-attribute, `data-changeview`, which could do _either_ a push or pop depending on the source order.

Start at the `changeView` method and inspect how `@$views`, `@$activeView`, and `$targetView` are used to select an action. Implement the proposed source-order behavior when `action` is omitted, then verify that a `data-changeview` attribute can trigger either push or pop based on that order.

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