Svg-painter:
- Clean up the JS, better names, etc.
- Convert the base64 encode/decode code from jQuery plugin to local use.
- Add missing icon colors for the default theme.
- Make it more error-proof.
Fixes #26333.

git-svn-id: https://develop.svn.wordpress.org/trunk@26601 602fd350-edb4-49c9-b593-d223f7449a82