Implement a rudimentary applets system (#804)

* Implement Player Select applet

* Initialize the Horizon system reference

* Tidy up namespaces

* Resolve nits

* Resolve nits

* Rename stack to queue

* Implement an applet FIFO

* Remove debugging log

* Log applet creation events

* Reorganise AppletFifo

* More reorganisation

* Final changes

Ryujinx.HLE/HOS/Applets/IApplet.cs

@@ -0,0 +1,13 @@
+using Ryujinx.HLE.HOS.Services.Am.AppletAE;
+using System;
+
+namespace Ryujinx.HLE.HOS.Applets
+{
+    interface IApplet
+    {
+        event EventHandler AppletStateChanged;
+
+        ResultCode Start(AppletFifo<byte[]> inData, AppletFifo<byte[]> outData);
+        ResultCode GetResult();
+    }
+}