Use a template to set the contents of the CommentEmails.

Add an admin editable Comment.vm template used to format the
contents of the comment emails.

Change-Id: Ic8e9cf6c3b60ae0c4a0e8a05537cf308a40ee694

gerrit-pgm/src/main/java/com/google/gerrit/pgm/init/SitePathInitializer.java

@@ -87,6 +87,7 @@ public class SitePathInitializer {
 
     extractMailExample("ChangeFooter.vm");
     extractMailExample("ChangeSubject.vm");
+    extractMailExample("Comment.vm");
     extractMailExample("Merged.vm");
 
     if (!ui.isBatch()) {