* Get rid of EchoBackend by separating responsibilities into smaller objects
* Move main fetchNotification logic from API to a more appropriate place
* Add more unit testing coverage
Change-Id: I42f4d7566543332588431c21c220c0d64d026b70
To test the HTML email:
1. install the latest version of php-mail and php-mail-mime package, they are required
by the core sendmail function to send HTML email
2. set $wgAllowHTMLEmail = true before loading Echo in LocalSetting.php
Change-Id: Ia4b98b14e135742b84f1b0e04589b0efdd24e954
