Instead of passing string, pass title revision object

... just like what was already being done for 'revision'

It will make things easier & more straightforward to deal with
extracting what we want from it, when we can do it all in 1 place.
E.g. truncating content is easier to do just in NotificationsController,
where we already have $wgContLang injected.

I also noticed there was an occurence of $title->getContent(), without
the format being specifically set to 'wikitext', which was a potential
issue that could case wikitext-like titles being parsed in notifications.

Change-Id: I87597d9060914fc0ac5304951b6d4b3b71f6051f
(bug 60906) Truncate content before storing event into DB

Because the event_extra column is limited in size, so we don't want
to store too much ;)

Bug: 60906
Change-Id: I0ee10904caaaadecf43c8c5440f901e6888809bb
Merge "Instead of passing string, pass title revision object"
Merge "(bug 60906) Truncate content before storing event into DB"