mediawiki.Title: Fix typo "add" in documentation

mediawiki.Title: Fix typo "add" in documentation

Follows-up 3d14628237.

* Put @class after the description for consistency with other
  classes and methods.
* Remove jscs:disable rule which was there for the illegal
  @constructor use (descriptions must go before a tag, not after).
  However JSDuck doesn't support descriptions before @constructor.
  It supports it with all other tags, however.

  It turns out, that @constructor doesn't support this because
  it is deprecated and predates that feature in JSDuck. Upstream
  documentation encourages authors to use @method instead.

Change-Id: Iba9fa5ae1fc8ece9ddff4aef8a3b4b59768fcaf0