MDL-66109 js: Upgrade to latest version of Shifter

This change bumps the version of Shifter that we use to the final
release - version 1.2.0.

I strongly doubt that there will be more releases, and this release was
over two years ago.

This version uses a newer version of Istanbul, and fixes to use that
specific version of Istanbul. As a result I have forked Shifter and
applied the Moodle Circular Dependency fixes there instead.

This version also inludes an upgrade to uglify from 1.3.x to 2.4.x. This
major upgrade includes a some changes to the built YUI module code.