various notification fixes

src/mail_templates/app_down-text.ejs

@@ -0,0 +1,19 @@
+Dear Cloudron Admin,
+
+The application '<%= title %>' installed at <%= appFqdn %> is not responding.
+
+This is most likely a problem in the application.
+
+To resolve this, you can try the following:
+
+* Check the app logs - https://docs.cloudron.io/apps/#log-viewer
+* Restart the app by opening the app's web terminal - https://docs.cloudron.io/apps/#web-terminal
+* Check the troubleshooting guidelines - https://docs.cloudron.io/troubleshooting/#unresponsive-app
+* Contact us in our Forum at https://forum.cloudron.io
+
+Powered by https://cloudron.io
+
+Don't want such mails? Change your notification preferences at <%= notificationsUrl %>
+
+Sent at: <%= new Date().toUTCString() %>
+