Update to support Cisco Codec External Sources using Essentials Room logic.

Adds new interface for Codecs IHasExternalSourceSwitching
Adds ability to set and clear External Sources in Cisco Spark device class
Adds ability to send sources from the source list to the Cisco Spark in the "EssentialsHuddleVtc1Room" room
[ ] still needs parsing when source is selected on the Cisco touch 10

PepperDashEssentials/UIDrivers/EssentialsHuddleVTC/EssentialsHuddleVtc1PanelAvFunctionsDriver.cs

@@ -1047,12 +1047,15 @@ namespace PepperDash.Essentials
 		/// </summary>
 		void SetupSourceList()
 		{
-				
+					
 			var inCall = CurrentRoom.InCallFeedback.BoolValue;
 			var config = ConfigReader.ConfigObject.SourceLists;
+			
+			
 			if (config.ContainsKey(_CurrentRoom.SourceListKey))
 			{
 				var srcList = config[_CurrentRoom.SourceListKey].OrderBy(kv => kv.Value.Order);
+				
 
 				// Setup sources list			
 				SourceStagingSrl.Clear();
@@ -1076,6 +1079,8 @@ namespace PepperDash.Essentials
 						b => { if (!b) UiSelectSource(routeKey); });
 					SourceStagingSrl.AddItem(item); // add to the SRL
 					item.RegisterForSourceChange(_CurrentRoom);
+					Debug.Console(1, "**** KEY {0}", kvp.Key);
+					
 				}
 				SourceStagingSrl.Count = (ushort)(i - 1);
 			}