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
Would you mind dropping the comment here? I think it's something PAD was using while he was working on it, but now I just see it as something that'll get outdated as we work on this