Grunt minify javascript proof of concept

I made this really as a proof of concept, but it worked to well I wanted to submit this pull so you could take a look.

What this does is adding two new grunt commands. `grunt concat` which concates a long list of .js-files into one single file (manager.js). The other command is `grunt uglify` which minifies manager.js into manager.min.js.

I've replaced the group minification in the manager and removed the .php-file that does this. It is (imo) redundant. I tried getting all the javascript-files into the minification, but it looks like it is impossible due to the way extjs and l18n is made possible in the manager. I guess that is the price you pay when you build everything around dynamic javscript-solutions.

Feel free to comment on this.

And please read the forum-thread: http://forums.modx.com/thread/91496/why-compress-css-and-compress-js-are-silly