Create Tags Management Stubs for Ember

closes #4260

- Adds "tags" route inside of the settings routes.
- Adds this route to router.js
- Links the route from the settings.hbs template
- Adds demo tags html in tag.hbs template
- Adds flag for tagsUI
I've done something like [this](http://ember.zone/handling-environment-data-with-ember-js/) before, and it works nicely. We could definitely make a beginner issue to implement that.

Would then be nice to have someone create a backend feature that automates creating those metas, rather than making a helper on a per-config basis.