Adding support for the .NET scripting background

Placed entirely behind a UNITY_EDITOR check because this particular code is only used from the editor. The UWP .NET libraries don't have the same support for Types class functionality, so rather than trying to update this to support the UWP version of types, we can drop the code in runtime environments.

Author: wiwei

Assets/MixedRealityToolkit/Attributes/MixedRealityExtensionServiceAttribute.cs

@@ -71,12 +71,17 @@ public MixedRealityExtensionServiceAttribute(
             PackageFolder = packageFolder;
         }
 
+#if UNITY_EDITOR
         /// <summary>
         /// Convenience function for retrieving the attribute given a certain class type.
         /// </summary>
+        /// <remarks>
+        /// This function is only available in a UnityEditor context.
+        /// </remarks>
         public static MixedRealityExtensionServiceAttribute Find(Type type)
         {
             return type.GetCustomAttributes(typeof(MixedRealityExtensionServiceAttribute), true).FirstOrDefault() as MixedRealityExtensionServiceAttribute;
         }
+#endif // UNITY_EDITOR
     }
 }