SideBySide2: Add shift-m to mark reviewed and open next file

In the old UI "M" marked the reviewed flag (if not already set)
and moved to the next file in the change. Implement a similar
behavior in the new SideBySide2 UI.

Bind as "shift m" instead of "M" due to vim mode using lowercase
"m" as a mark character, which some users may actually use to make
bookmarks during a review.

Change-Id: I1e7780e6265fa3380aae09c034583dec7ec4830a

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/Header.java

@@ -310,6 +310,18 @@ class Header extends Composite {
     }
   }
 
+  Runnable reviewedAndNext() {
+    return new Runnable() {
+      @Override
+      public void run() {
+        if (Gerrit.isSignedIn()) {
+          reviewed.setValue(true, true);
+        }
+        navigate(Direction.NEXT).run();
+      }
+    };
+  }
+
   String getNextPath() {
     return nextPath;
   }