Implement new edit workflow.

* Remove title from Edit activity
* Change actionbar button to be state-dependent ("Next"/"Done")
* Remove icon from actionbar button
* Implement clickable edit summary tags
* Show edit summary, license, and preview on one screen
* Remove CTA to sign in when saving

Change-Id: Ied20be64d35d1038937e96cb6a809a994c8b8035