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/Services/Am/AppletAE/AppletFifo.cs

@@ -0,0 +1,79 @@
+using System;
+using System.Collections;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+
+namespace Ryujinx.HLE.HOS.Services.Am.AppletAE
+{
+    internal class AppletFifo<T> : IEnumerable<T>
+    {
+        private ConcurrentQueue<T> _dataQueue;
+
+        public int Count => _dataQueue.Count;
+
+        public AppletFifo()
+        {
+            _dataQueue = new ConcurrentQueue<T>();
+        }
+
+        public void Push(T item)
+        {
+            _dataQueue.Enqueue(item);
+        }
+
+        public T Pop()
+        {
+            if (_dataQueue.TryDequeue(out T result))
+            {
+                return result;
+            }
+
+            throw new InvalidOperationException("FIFO empty.");
+        }
+
+        public bool TryPop(out T result)
+        {
+            return _dataQueue.TryDequeue(out result);
+        }
+
+        public T Peek()
+        {
+            if (_dataQueue.TryPeek(out T result))
+            {
+                return result;
+            }
+
+            throw new InvalidOperationException("FIFO empty.");
+        }
+
+        public bool TryPeek(out T result)
+        {
+            return _dataQueue.TryPeek(out result);
+        }
+
+        public void Clear()
+        {
+            _dataQueue.Clear();
+        }
+
+        public T[] ToArray()
+        {
+            return _dataQueue.ToArray();
+        }
+
+        public void CopyTo(T[] array, int arrayIndex)
+        {
+            _dataQueue.CopyTo(array, arrayIndex);
+        }
+
+        public IEnumerator<T> GetEnumerator()
+        {
+            return _dataQueue.GetEnumerator();
+        }
+
+        IEnumerator IEnumerable.GetEnumerator()
+        {
+            return _dataQueue.GetEnumerator();
+        }
+    }
+}