Re-added uglify to build task.

Uglification (beyond minification) can improve performance of the JavaScript parser/compiler at runtime, due to consecutive `var` statements, removal of duplicate variables, AST code logic optimizations, etc.

Uglification is only enabled for the default `grunt build` task, because it would needlessly slow down realtime development.

Lastly, we only care for uglification, not for minification.  Therefore, uglify is configured to beautify the code after performing optimizations.