Improvements to hover and focus states on the adminbar:

* Add a clear hover state for top-level links in the adminbar.
* Add :focus styles to the adminbar for keyboard accessibility.
* Ensure that the username link in the profile submenu gets a :hover style.
* Add adminbar hover styles to color schemes.
* Set -webkit-font-smoothing to subpixel-antialiased on the adminbar so that Safari doesn't switch to standard antialiasing on mouseover.

Fixes #26152, props ryelle.



git-svn-id: https://develop.svn.wordpress.org/trunk@26407 602fd350-edb4-49c9-b593-d223f7449a82