Refactor TextEditorComponent and TextEditorWithNonEditableComponent

* Use of `contentEditable` for non editable pills.
* All tests for TextEditorComponent are passing
* Popover tests are passing

The text editor components are currently not cross browser compatible. The best solution would probably be to rely on a 3rd party library and to only wrap them for Ember.

All that code needs more refactoring / cleaning.

@azirbel @addepar-andy @igillis @Dylnuge 
Might be nice to separate the `KEY_CODES` constant from the class so we can use it in other places like the popover line above.