Dashicons: Include the easy-access classes for plugins

[dd32]

Currently the version of Dashicons in core doesn't include the easy-access/easy-use CSS classes such as .dashicons and .dashicon-wordpress, which forces themes to use the glyphs directly by specifying the fonts and content:'\f155';.

Instead, we should include the full set of icon classes as visible within the Dashicons CSS: ​https://github.com/melchoyce/dashicons/blob/master/css/dashicons.css

[melchoyce]

I kind of guessed on some of the class names — I'd appreciate a second look to make sure everything I've named them makes sense.

[dd32]

26227.diff​ is the extra rules.

The class names are visible within there, and also on the demo site here: ​http://melchoyce.github.io/dashicons/

I personally haven't seen any I disagree with, but it'd be helpful if others could comb through it as well.

[nacin]

In 26547:

Add dashicons CSS classes for easy access by plugins and themes.

props dd32.
fixes #26227.

[melchoyce]

In 26227.2.diff​, I updated the following icon class names:

Old	New
dashicons-admin-site	dashicons-admin-network
dashicons-site	dashicons-admin-site
dashicons-gauge	dashicons-admin-dashboard
dashicons-admin-dashboard	dashicons-admin-home
dashicons-camera2	dashicons-camera
dashicons-imgedit-undo	dashicons-undo
dashicons-imgedit-redo	dashicons-redo
dashicons-xit	dashicons-dismiss
dashicons-arrow-up	dashicons-upload
dashicons-arrow-down	dashicons-download
dashicons-network	dashicons-networking
dashicons-jobs-developers	dashicons-hammer
dashicons-jobs-designers	dashicons-art
dashicons-jobs-migration	dashicons-migrate
dashicons-jobs-performance	dashicons-performance

Also:

• imgedit --> image, write out full name (rleft --> rotate-left)
• graphs to --> chart-bar, chart-line, chart-area, chart-pie
• change everything with 1/2/3 to alt, alt-2
• change all arr to arrow
• remove twitter-alt b/c it's not correct branding

I also updated the data-uri for the font based on the latest version of dashicons.

[nacin]

In 26752:

Updates to Dashicons classes.

props melchoyce.
fixes #26227.