Initial JSDuck implementation

* Adding configuration files for jsduck.
* Fixing our previously undocumented code documentation to comply
  with jsduck specifications
  .. for the following modules:
  - mediawiki
  - mediawiki.Title
  - mediawiki.util
  - mediawiki.notification
  - mediawiki.api (and plugins thereof)
  - jquery.localize

I've choose these to show as many different examples for
different types of modules and methods that we encounter
in our code base.

Hopefully with this as a start it will be easy for other people
to extend the documentation for most (if not, all) other modules
we have in MediaWiki core.

Change-Id: Ieb8c5d2d2cb4672f1d6abc3f865c6fb1470d8feb
Merge "Initial JSDuck implementation"