Options for callbacks, invalidating

Adds `Transitioner.setOptions` including `before` and `after` callbacks, and a boolean `redrawAfterTransition` for whether or not  it should invalidate once the transition ends.

This lets the app control things like adding extra classes, etc. Also combining `redrawAfterTransition = false` with:

```
  after: ->
    next = $('.next')
    $('.current').removeClass('current').addClass('next')
    next.removeClass('next').addClass('current')
```

Reuses the DOM elements without re-rendering their contents.