Refactor of dashboards

* Remove dashboards from Configs().Dashboards
* Remove dashboard.config XML file & associated code reading from XML
* Load Dashboards from TypeLoader into a CollectionBuilder
* Load merge/concat C# Dashboard Types with package.manifest
* Add buildercolletion to an extension method on Composition

src/Umbraco.Web/Models/ContentEditing/DashboardControl.cs

@@ -1,19 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Runtime.Serialization;
-using System.Text;
-using System.Threading.Tasks;
-
-namespace Umbraco.Web.Models.ContentEditing
-{
-    [DataContract(Name = "control", Namespace = "")]
-    public class DashboardControl
-    {
-        [DataMember(Name = "path")]
-        public string Path { get; set; }
-
-        [DataMember(Name = "caption")]
-        public string Caption { get; set; }
-    }
-}