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
This is pretty much a straight c/p from somewhere else, right? Would be sweet if we could abstract it a little more, but no biggy....