mediawiki.action.edit.preview: Fire "wikipage.content" mw.hook

mediawiki.action.edit.preview: Fire "wikipage.content" mw.hook

The mw.hook framework was added in 2e97025 and it also added
an example event ("wikipage.content") but this was never
actually fired anywhere other than for the initial load.

This will finally make things like jquery.tablesorter and
jquery.makeCollapsible work in live preview.

Also:

* Deprecate non-standard jQuery events triggered on jQuery
  wrapper around the "mw" object.

Bug: 33399
Change-Id: Ic516b3a01b4c1510cbe5f2de2998ad8275ecc607