When buttons changed to flexbox they lost some alignment properties. This change makes the container for the empty content state use a flexbox container and align its containing items correctly. Also removes some old media queries which are no longer needed.
No issue
- Move editor-base-view mixin into editor/edit view
- Also deletes mobile views and modifies files that were using it
- Helps pave the way for Ember 2.0, where views do not exist
