Updating to UglifyJS2

Updating to v2.x series of UglifyJS2 (see https://github.com/mishoo/UglifyJS2) which also requires some changes in our `run.py` due to a slightly different commandline for UglifyJS2 (see http://lisperator.net/blog/should-you-switch-to-uglifyjs2/). This update generates a few WARN messages when using `./run.py -m` (originating from UglifyJS2).

Note that you may need to wipe your current `./node_modules/` folder, to ensure that `npm` collects the latest version; otherwise, you may see some error regarding a "require" of "../tools/node" (or something like that).