Proposal to change the headings hierarchy in the Mobile section

[afercia]

Splitting this out from #4110.

There's no much content in this page, however there's room for improvements for better SEO and accessibility:

As mentioned in #4112 the logo shouldn't be a h1. The main topic in this page is "WordPress Mobile Apps" and that should be the only h1 in the page.

[dufresnesteven]

Need to patch wp4.css:

#headline h2, 
#headline .heading {
    ... 
}

#headline .heading {
    font-weight: normal;
}

Change <h2> to <h1 class="heading">.

The style fix to wp4.css will also solve the same problem with https://meta.trac.wordpress.org/ticket/4122

[dd32]

In 9718:

Style: Update the styling for the /hosting and /mobile pages to use a better heading structure.

See #4116, #4122.

[dd32]

That commit brought with it a bunch of things that have been missed in the past, due to the Grunt build process not being run..

• RTL styles updated
• browser back-compat added, etc.

I also chose to match the existing heading styling for the hosting page (#4112) and added the proper namespacing for the page-specific styles..