more complete bootstrap 3 RC 1 support

Limitations:
* Escape doesn't dismiss modals
* Input on modals doesn't get focus
* Default styling is now dark to match btn-default
* Formatting buttons don't show whether they are active or not since I removed `a.btn.wysihtml5-command-active` style. The correct way to do this would be to set `class='active'` on the button when `wysihtml5-command-active` but I don't know how to do that.
* Probably other things, but it works and doesn't look bad.