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 actually thought this had been changed to use the API, but apparently not. The extra helpers are a bit of overkill I think - but that's definitely a separate issue to fix