Callback to view should be more descriptive

[gregorymarkthomas]

Right now it is onSuccess and onError.
But those do not describe when these should occur.
Perhaps (re)use onViewUpdated() and so on.

[gregorymarkthomas]

The developer is able to make their own function name when they create the Backstack objects in the view. Perhaps the documentation in backstack.js should be more descriptive.