HG-199

POSTPONED, do not merge, need bit more work.


Currently `Random Page` button in Mercury goes to MW `Special:Random` page. We want to change it and use Ember's magic there. The changes below use new entry-point on MW side implemented in: https://github.com/Wikia/app/pull/5113 and are as follow:
* Hapi entry point for random page,
* EmberJS changes on front-end side (new `randomPage` route, new custom action in `ApplicationRoute`, changes in `ArticleModel` and in local navigation template).

**TODO:**
- [x] unit tests fixes,
- [ ] new unit tests,
- [ ] fix first visit,
- [ ] check how to pass model into article view instead of sending 2 requests,
- [ ] remove promises in `ArticleModel` and test if it still works -- it should since `$.ajax()` returns a promise
- [ ] change `/random` route to `/article/random`,
- [ ] create a new interface for the object passed as parameter in `ArticleModel::buildArticleUrl()`