feat: refactor LoadRooms method

In order to facilitate using custom messengers, I added an interface, `IStandardMobileControl` that devices or rooms can implement if they should use the standard/existing MobileControl messengers. If a room or device wants to implement non-standard messengers, or is a new type of device that doesn't yet have a corresponding messenger in the Mobile Control plugin, do NOT implement this interface and MC won't attempt to build a messenger for it.

src/PepperDash.Essentials.Core/DeviceTypeInterfaces/IMobileControl.cs

@@ -5,6 +5,13 @@ using PepperDash.Core;
 
 namespace PepperDash.Essentials.Core.DeviceTypeInterfaces
 {
+    /// <summary>
+    /// Use this interface on a device or room if it should use default Mobile Control messengers
+    /// </summary>
+    public interface IStandardMobileControl : IKeyed
+    {
+    }
+
     /// <summary>
     /// Describes a MobileControlSystemController
     /// </summary>