[ticket/11103] Move all email templates to the email/ directory & prep short

Prepare short email templates (to be used in jabber)

PHPBB3-11103

phpBB/language/en/email/short/topic_approved.txt

@@ -0,0 +1,11 @@
+Subject: Topic approved - "{TOPIC_TITLE}"
+
+Hello {USERNAME},
+
+You are receiving this notification because your topic "{TOPIC_TITLE}" at "{SITENAME}" was approved by a moderator or administrator.
+
+If you want to view the topic, click the following link:
+{U_VIEW_TOPIC}
+
+
+{EMAIL_SIG}