[RFR] Add build process

- [x] Use requirejs to build files
- [x] Use ngmin to allows minification
- [x] Concatenate files
- [x] Allows to use external config file
- [x] Add minification process
- [x] Fix tests

Usage :
```js
(function() {
    "use strict";

    var app = angular.module('myApp', ['ng-admin']);

    app.config(function(NgAdminConfigurationProvider, Application, Entity, Field, Reference, ReferencedList, ReferenceMany) {

        var post = Entity('posts')
             .label('Posts')
            .order(1)
            .dashboard(null)
            .perPage(10)
            .pagination(pagination);

        var app = Application('ng-admin backend demo')
            .baseApiUrl('http://localhost:3000/')
            .addEntity(post);

        NgAdminConfigurationProvider.configure(app);
    })
})();