XD-1328 Modularize UI (Part 1)

- Add RequireJS support for the main app
 - Added RequireJS configuration for xdAdmin app
 - Define AMD modules
 - Bootstrap app with these modules
 - Disabled minification of js files for now

- Updated/modified grunt tasks
 - Channged yeoman.app -> xd.app
 - Removed unused grunt tasks
 - Modified bower components targetDir to use lib/

TBD:
 - Support minification of JS files with requireJS optimizer
 - Fix karma unit tests and add requireJS support
 - Modularize controllers and services further to define
   individual AMD modules for each controller/service.