use FxA web flow for forgot pin (bug 1033711)

This doesn't seem like the right place to put navigation logic. I think you want to make data changes to the models and let the controllers do the navigating.

Maybe allow ``logged_in`` event handlers deal with the event just like before, just introduce a data model change for them to react to. Something like ``app.pin.set('needs_reset', true)`` on [models/pin](https://github.com/washort/spartacus/blob/fxa-fxos2/public/js/models/pin.js). Then add an if statement to handle the data and navigate to the right page in the [existing handlers](https://github.com/washort/spartacus/blob/fxa-fxos2/public/js/views/page.js#L99).