Document most core interfaces

Oqtane.Shared/Interfaces/IService.cs

@@ -1,7 +1,9 @@
-namespace Oqtane.Modules
+namespace Oqtane.Modules
 {
+    /// <summary>
+    /// Empty interface used to decorate module services for auto registration
+    /// </summary>
     public interface IService
     {
-        // empty interface used to decorate module services for auto registration
     }
 }