Post format UI refresh.

* Post format switcher does not go away after clicking
* Refresh of format switcher style
* Highlighting of active post format
* Prompt text goes under the switcher
* Better animations

see #24046. props wonderboymusic, johnjamesjacoby, aaroncampbell, PeteMall.

Also, because I forgot it on [24006]: props saracannon.

git-svn-id: http://core.svn.wordpress.org/trunk@24098 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Remove unused variable and CSS class. see #24046.

git-svn-id: http://core.svn.wordpress.org/trunk@24099 1a063a9b-81f0-0310-95a4-ce76da25c4cd