Uses the class EchoDiscussionParser to understand actions taken on
vanilla MediaWiki discussion pages.
Currently notifies on these occasions:
* A new comment is added to a discussion on your talk page or that
you have participated in.
* A new topic is added to your talk page.
There are vague plans to expand to these classes of events:
* Your comment is edited or removed.
* A large section is moved to your talk page.
and these classes of users:
* Users watching discussion pages.
Change-Id: Ie6cae76ed2e0ecf607059e39ac1aa480a275ec89
