Implement unified API controller pattern

EstusShots.Shared/Interfaces/IApiParameter.cs

@@ -0,0 +1,12 @@
+namespace EstusShots.Shared.Interfaces
+{
+    /// <summary>
+    /// Marks a class that can be used as a parameter for API requests
+    /// </summary>
+    public interface IApiParameter { }
+    
+    /// <summary>
+    /// Marks a class as response type that is returned from API requests
+    /// </summary>
+    public interface IApiResponse { }
+}