Add an "Unsubmitted" button to the Differential persistent header

Summary: Ref M1476. Same as D18070 but that did most of the magic.

Test Plan: {F4987961}

Reviewers: chad

Reviewed By: chad

Differential Revision: https://secure.phabricator.com/D18071

webroot/rsrc/js/application/diff/DiffChangeset.js

@@ -451,7 +451,8 @@ JX.install('DiffChangeset', {
                 end: block.items[jj]
               },
               attributes: {
-                unsaved: inline.isEditing()
+                unsaved: inline.isEditing(),
+                unsubmitted: inline.isDraft()
               }
             };