Dashicons support for WordPress 3.8

[johnjamesjacoby]

Let's use the Buddicons supplied by Ben for top level menus and the components settings page.

Haven't figured out a way to make it backwards compatible without having separate stylesheets and making a decision in PHP, which seems like more trouble than it's worth for icons IMO.

[boonebgorges]

Using the technique suggested here by nacin ​http://make.wordpress.org/ui/2013/11/19/targeting-the-new-dashboard-design-in-a-post-mp6-world/ (targeting the old versions rather than new ones), 5291.02.patch provides a CSS-only method of backward compatibility.

I also took the liberty to fix the Components icons for Firefox. It turns out that, because FF doesn't support background-position-x and background-position-y, they have never worked properly! I'm pretty shocked this has never been reported. Anyway, simple fix.

This is looking good and I don't see a problem including it in 1.9, but I would like to have another set of eyes on it (especially if you can check on a 3.7 *and* a 3.8 rig).

[johnjamesjacoby]

In 7667:

WordPress 3.8 support for top level menu icons. Props boonebgorges. Fixes #5291.