Fixes toolbar positioning on edges

Fixed positioning on edges, but the arrow is static. Needs to be reworked because you can't select css pseudo elements in javascript (they are not in the DOM).

![medium-toolbar-right](https://f.cloud.github.com/assets/1269436/1263605/2b9a1fca-2c53-11e3-82d4-dc709ab7ee2e.png)