Sync with UI repository and wire up dummy views for missing prototypes

This brings pretty much everything across from the UI repo.

* Adds login view
* Adds register view
* Adds sets view
* Handle modals
  * Separate views for each modal
  * ModalController to handle showing modals
* Wiring up JS for edit post and add to set views
  * Note the edit post JS is broken (already was) but we'll fix that when wiring edit post up properly
* Update CSS/SCSS from UI repo
* Add/remove images from UI repo