Final SVG painter fixes.
 * wp.svgPainter and now moved to wp-admin.
 * Restore !important background-image handling.
 * Delay executing the IE9-specific base64 code if we don't need it.
 * Make painted icons lose their color after hover at the same speed as dashicons (100ms).

props azaozz.
fixes #26333.


git-svn-id: https://develop.svn.wordpress.org/trunk@26693 602fd350-edb4-49c9-b593-d223f7449a82