Appointment tags

Contains
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* Show individual appointment tags
* Tag and Untag appointments

TODOs
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* 
Re-render appointment page after tag change (works on DELETE, not on POST)
 done with `property('model.tags.@each')`
* Check a proper way for handling  the delete/lookup *EDIT* should be ok for now - Ember Data doesn't support nested REST APIs yet.
* Extract back the tag/untag actions and the template to AppointmentTagController and render it as such.
* 
Load the tags and filter them on first render, currently they show up on second render/click
 had to attach `allTags.@each` to the `property(...)` to observe to the change.

@sciritai would be good if you can advise me on the TODOs...

Depending on https://github.com/CrazyHorseHQ/smart_app/pull/32