Added the emailReviewers as a global capability

This adds functionality to deny the emailing of reviewers to certain
groups.  This will replace the emailOnlyAuthors flag on the
AccountGroup.

Change-Id: If3697e88df50e0b0256b5b6a1ea810343124b96f

gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/AdminConstants.properties

@@ -128,6 +128,7 @@ capabilityNames = \
   createAccount, \
   createGroup, \
   createProject, \
+  emailReviewers, \
   flushCaches, \
   killTask, \
   priority, \
@@ -140,6 +141,7 @@ administrateServer = Administrate Server
 createAccount = Create Account
 createGroup = Create Group
 createProject = Create Project
+emailReviewers = Email Reviewers
 flushCaches = Flush Caches
 killTask = Kill Task
 priority = Priority