Create a version of mediawiki.skinning.content for Parsoid HTML

The provides a transitional central content styling module for all
consumers of Parsoid's HTML+RDFa, to avoid local duplication (and
variation) of these rules in each of the consuming applications such as
Parsoid's read service[0], VisualEditor[1], MobileFrontend[2], Kiwix[3],
Flow[4] and others.

In a short while (probably before MW 1.24 branches), we expect to switch
over the primary read HTML to Parsoid- rather than MWParser-generated,
at which time this HTML will become the core for MediaWiki's content
styling, with skins able to over-ride or augment this styling as they see
fit.

[0] http://parsoid-lb.eqiad.wikimedia.org/enwiki/Foobar?oldid=608091782
[1] http://en.wikipedia.org/wiki/Foobar?oldid=608091782&veaction=edit
[2] http://en.m.wikipedia.org/wiki/Foobar?oldid=608091782
[3] http://www.kiwix.org/wiki/Main_Page
[4] http://en.wikipedia.org/wiki/Wikipedia_talk:Flow/Developer_test_page

Change-Id: I400336c12d58308d7177b24180693874effadf69
Merge "Create a version of mediawiki.skinning.content for Parsoid HTML"