Grunt minify and concatenate fixed

With recent changes possibility to create minified and concated version for aura app was lost. I've added my proposal to solve that for app.js entry file. This approach works for jquery. With zepto there are issues because of incompability with jQuery UI and full calendar.
Current approach doesn't include widgets in concatenation. This is because it requires some discussion. In my opinion there should be one file per widget as output in distribution version. There can be also some issues with sandbox per widget approach. Sandbox itself can be easily removed from grunt requirejs job, but I'm afraid relative paths approach can be roadblock for r.js.

I also upgraded following libraries:
- jQuery
- lodash
- backbone
- requireJS