Merge changes from topic 'revert-of'

* changes:
  Add revertOf to ChangeIndex
  Add revertOf to ChangeInfo and populate it when /revert is called
  Add revertOf to ReviewDb and NoteDb

gerrit-extension-api/src/main/java/com/google/gerrit/extensions/common/ChangeInfo.java

@@ -48,6 +48,7 @@ public class ChangeInfo {
   public Boolean isPrivate;
   public Boolean workInProgress;
   public Boolean hasReviewStarted;
+  public Integer revertOf;
 
   public int _number;