Only show "Add New Theme" block on Manage Themes screen if not Multisite and the user can install themes.

props markoheijnen.
see #25948.
Built from https://develop.svn.wordpress.org/trunk@26288


git-svn-id: http://core.svn.wordpress.org/trunk@26193 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Cleanup on inputs:

* Remove the !important from checkbox and radio border color
* Remove the redundant #wpbody select rule
* Add checkbox and radio inputs to the standard :focus style rules for inputs
* Remove custom border and box shadow styles from .login inputs
* Don't remove the default outline from select elements since webkit doesn't allow borders on selects

Fixes #26120.


Built from https://develop.svn.wordpress.org/trunk@26289


git-svn-id: http://core.svn.wordpress.org/trunk@26194 1a063a9b-81f0-0310-95a4-ce76da25c4cd