Require REVIEWED option to retrieve reviewed flag from /changes/

Setting the reviewed flag in the ChangeInfo JSON requires loading
all ChangeMessage entities for the current patch set, sorting them
by the date, and filtering to find an entry by the calling user.

This information is only valid for the caller.  When viewing another
user's dashboard changes are marked bold if the *caller* has not
reviewed the change, not if the owner of the displayed dashboard has.
This is outright misleading.  On dashboards that are not the callers
highlighting is now disabled and the reviewed flag is not computed.

The reviewed flag and highlighting is not used in search results,
such as All > Open.  Computing the reviewed flag for the signed
in caller is a waste of server CPU resources.  As the queries are
performed sequentially during JSON result construction, this is
also very slow on slower database environments like gerrit-review.

Disable the recursive query logic behind an option in the request,
significantly cutting costs for common queries.

Change-Id: If8acbe430e8803e1d9cfcb747dfe28713c1b6da4

gerrit-common/src/main/java/com/google/gerrit/common/changes/ListChangesOption.java

@@ -40,7 +40,10 @@ public enum ListChangesOption {
   MESSAGES(9),
 
   /** Include allowed actions client could perform. */
-  CURRENT_ACTIONS(10);
+  CURRENT_ACTIONS(10),
+
+  /** Set the reviewed boolean for the caller. */
+  REVIEWED(11);
 
   private final int value;