Add minified browser build in gruntfile

After browser build is complete, we're invoking uglify-js to create a minified version for deployment to CDNs.

Don't worry about all the apparent changes to the package.json file.  All I did was `npm install --save-dev uglify-js`.  It was npm that did all of the rearranging.  Nothing appears to be broken. 

The minification is done with the default settings, which is just fine for most purposes.  If anyone really wants to try to squeeze a few more bytes out of it, you can play with the settings in uglify's API.