Create new frontend powered by Ember.js

This will be more or less a rewrite of sentry.web.

The plan is to migrate *everything into client side templates (though at first, we might leave the settings/pages with forms on the server). We'll power it off the API, which the initial framework (DRF) was recently landed.

https://github.com/stefanpenner/ember-app-kit
https://github.com/rpflorence/ember-tools
