Use a template to set the footer on ChangeEmails.

Add an admin editable ChangeFooter.vm template used to
format the footer in ChangeEmails.

Change-Id: I8f6f80b7a3e1fdb39ee1ea20aa84738286bce826

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

@@ -85,6 +85,7 @@ public class SitePathInitializer {
     extract(site.gerrit_sh, Init.class, "gerrit.sh");
     chmod(0755, site.gerrit_sh);
 
+    extractMailExample("ChangeFooter.vm");
     extractMailExample("ChangeSubject.vm");
     extractMailExample("Merged.vm");