Content selector

Implemented single item selector for generic content.

To add it to a widget
1. Create MVC widget
2. Add new designer view
  In it place this tag <content-selector selecteditemid="selectedId"      itemtype="Telerik.Sitefinity.News.Model.NewsItem"></content-selector> 
3. Add .json file for loading scripts in the Views/YourWidget folder. In the file require the following scripts
        "Mvc/Scripts/Angular/angular-resource.min.js",
	"Services/services.js",
	"Services/generic-data-service.js",
	"Selectors/selectors.js",
	"Selectors/content-selector.js"
4. Add file with custom controller in Mvc/Scripts/YourWidget. In its beginning add the following lines
    var designerModule = angular.module('designer');
    angular.module('designer').requires.push('selectors');