Add minify/uglify options to Gulp config

The compiled `picard.js` file currently equates to about 691KB uncompressed. When compressed with something like `uglify`, it comes in at about 260KB.

Of course, in any production environment, we would want it compressed. It would be super to have some additional `gulp` commands that allow you to build for production.

Start with the Gulp config and the existing commands that build the compiled picard.js file; compare the current output with a compressed production build. Done means production-oriented Gulp commands can generate a compressed artifact, with the result checked against the reported size reduction.

Written by the indexing model from the issue text.