Convert change notification email templates to Soy

Convert the templates used by subclasses of ReplyToChangeSender from
Velocity to Soy. Modify the way reviewer lists are generated for Soy
templates to avoid including the change owner in the salutation line of
ReplacePatchSet emails.

Feature: Issue 4345
Change-Id: I827fae73a81164540b399493b5b67ceb65acb362

gerrit-acceptance-tests/src/test/java/com/google/gerrit/acceptance/server/change/CommentsIT.java

@@ -544,6 +544,7 @@ public class CommentsIT extends AbstractDaemonTest {
         + "\n"
         + "PS2, Line 2: nten\n"
         + "typo: content\n"
+        + "\n"
         + "\n");
   }