Adds Randomize button that:
- Randomizes start and finish marker on level 9.
- Randomizes entire maze on level 10.

The randomizeMarkers() method and associated CSS were restored from revision 611.
Review URL: https://codereview.appspot.com/7476044

git-svn-id: http://blockly.googlecode.com/svn/trunk@683 c400ca83-b69d-9dd7-9705-49c6b8615e23