Better support for user accounts (#349)

* Better support for user accounts

* Nits

* Check for invalid ids

Ryujinx.HLE/OsHle/SystemState/AppletStateMgr.cs

@@ -0,0 +1,62 @@
+using Ryujinx.HLE.OsHle.Handles;
+using Ryujinx.HLE.OsHle.Services.Am;
+using System;
+using System.Collections.Concurrent;
+
+namespace Ryujinx.HLE.OsHle.SystemState
+{
+    class AppletStateMgr : IDisposable
+    {
+        private ConcurrentQueue<MessageInfo> Messages;
+
+        public FocusState FocusState { get; private set; }
+
+        public KEvent MessageEvent { get; private set; }
+
+        public AppletStateMgr()
+        {
+            Messages = new ConcurrentQueue<MessageInfo>();
+
+            MessageEvent = new KEvent();
+        }
+
+        public void SetFocus(bool IsFocused)
+        {
+            FocusState = IsFocused
+                ? FocusState.InFocus
+                : FocusState.OutOfFocus;
+
+            EnqueueMessage(MessageInfo.FocusStateChanged);
+        }
+
+        public void EnqueueMessage(MessageInfo Message)
+        {
+            Messages.Enqueue(Message);
+
+            MessageEvent.WaitEvent.Set();
+        }
+
+        public bool TryDequeueMessage(out MessageInfo Message)
+        {
+            if (Messages.Count < 2)
+            {
+                MessageEvent.WaitEvent.Reset();
+            }
+
+            return Messages.TryDequeue(out Message);
+        }
+
+        public void Dispose()
+        {
+            Dispose(true);
+        }
+
+        protected virtual void Dispose(bool Disposing)
+        {
+            if (Disposing)
+            {
+                MessageEvent.Dispose();
+            }
+        }
+    }
+}