Make the responsive layout behave better when the user zooms the page:

* Change the smartphone media query from 480 to 600px so it captures large screen phones in landscape mode.
* Set #wpadminbar to position: absolute at smartphone sizes so it scrolls with the page, freeing up the viewport.
* Remove the transition states on #adminmenu for better performance on mobile devices
* Make the responsive sidebar scroll with the page instead of using a fixed position
* Remove the -webkit-overflow-scrolling rule that was disabling scroll-to-top when tapping the iOS status bar.
* Remove unnecessary zoom declaration from -ms-viewport.

See #25858.



git-svn-id: https://develop.svn.wordpress.org/trunk@26373 602fd350-edb4-49c9-b593-d223f7449a82