Add Post Format icons to the old radio chooser

[markjaquith]

Little post format icons should be added to the old radio chooser, like MelChoyce mocked up:

[ryelle]

Added spans using the classes from the post list table icons, so I also had to remove the element from the selectors in CSS & add a format-standard class. I also added more space around the options.

[helen]

Would it make more sense to change the sprites to be vertical and nix the empty span? I'd also rather add a selector or name it better rather than shoe-horning in one that isn't very semantic to use.

[kovshenin]

Refreshed in 24519.2.patch​

[helen]

In 24426:

Change the post format icons sprite to be vertical rather than horizontal in order to allow it to be used for wider items such as labels. RTL tweak for the icon in the posts list table. See #16047, #24519.

[helen]

In 24429:

Add post format icons to the radio chooser. This also trims empty margins from the sprites to make them usable in RTL and make positioning numbers more sane. props ryelle, kovshenin for the initial patch. fixes #24519.