Use a template to set the contents of the MergedEmails.

Add an admin editable Merged.vm template used to format the
contents of the merged change emails.

Change-Id: I79823c2135383a7dbf7f245abea3d693db025150

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

@@ -86,6 +86,7 @@ public class SitePathInitializer {
     chmod(0755, site.gerrit_sh);
 
     extractMailExample("ChangeSubject.vm");
+    extractMailExample("Merged.vm");
 
     if (!ui.isBatch()) {
       System.err.println();