Switch our JavaScript compressor to UglifyJS.
Switch our JavaScript compressor to UglifyJS.

We were using jsmin for compressing JavaScript, but this has some
annoying license issues, and flat-out breaks with jquery.cookie. It's
also just not very good compared to modern tools.

This change switches to using UglifyJS. Uglify has the advantage of
being used and well-tested by large numbers of projects, including
jQuery. It's easy to install (npm install uglify-js), and since we use
npm for other tools (lessc, require.js soon), it's nice and consistent.

Another good option would have been Closure, but Closure's really mad at
a lot of our code (probably worth looking into anyway). It also seems to
have some inconsistent installation experiences on MacOS, from when I
first installed it. For those reasons, I'm erring in the favor of npm,
given that we already require it. (Hopefully this also make life a
little easier for our packagers.)

With this change, I can build working JavaScript bundles again.

sgallagher/reviewboard,custode/reviewboard,bkochendorfer/reviewboard,beol/reviewboard,reviewboard/reviewboard,bkochendorfer/reviewboard,KnowNo/reviewboard,custode/reviewboard,custode/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,1tush/reviewboard,custode/reviewboard,1tush/reviewboard,reviewboard/reviewboard,davidt/reviewboard,brennie/reviewboard,bkochendorfer/reviewboard,davidt/reviewboard,sgallagher/reviewboard,1tush/reviewboard,1tush/reviewboard,1tush/reviewboard,KnowNo/reviewboard,sgallagher/reviewboard,brennie/reviewboard,brennie/reviewboard,KnowNo/reviewboard,1tush/reviewboard,1tush/reviewboard,1tush/reviewboard,chipx86/reviewboard,bkochendorfer/reviewboard,chipx86/reviewboard,davidt/reviewboard,beol/reviewboard,brennie/reviewboard,1tush/reviewboard,beol/reviewboard,chipx86/reviewboard,KnowNo/reviewboard,beol/reviewboard,chipx86/reviewboard,sgallagher/reviewboard,davidt/reviewboard