Better support for user accounts (#349)

* Better support for user accounts

* Nits

* Check for invalid ids

Ryujinx.HLE/OsHle/SystemState/UserProfile.cs

@@ -0,0 +1,36 @@
+using System;
+
+namespace Ryujinx.HLE.OsHle.SystemState
+{
+    class UserProfile
+    {
+        private static readonly DateTime Epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+
+        public UserId Uuid { get; private set; }
+
+        public string Name { get; private set; }
+
+        public long LastModifiedTimestamp { get; private set; }
+
+        public OpenCloseState AccountState    { get; set; }
+        public OpenCloseState OnlinePlayState { get; set; }
+
+        public UserProfile(UserId Uuid, string Name)
+        {
+            this.Uuid = Uuid;
+            this.Name = Name;
+
+            LastModifiedTimestamp = 0;
+
+            AccountState    = OpenCloseState.Closed;
+            OnlinePlayState = OpenCloseState.Closed;
+
+            UpdateTimestamp();
+        }
+
+        private void UpdateTimestamp()
+        {
+            LastModifiedTimestamp = (long)(DateTime.Now - Epoch).TotalSeconds;
+        }
+    }
+}