Implement new popovers

No issue

Implements a new popover component (not to be confused with what are now called dropdowns [menus])

Todo:

- [x] Emberify
- [x] Get checked over by people with Über Ember skilz
- [ ] Remove temporary code in debug view (when the rest of the code is all good)

Thanks for moving this to a new file. Would you just add a single comment saying "this is used for..." at the top, since we no longer have the context of it being in the same file as the initializer?