Removed NioTSO client and server

- NioTSO client isn't needed because we're using RayLib
- Added FreeSO's API server to handle most backend operations

server/tso.common/Security/AvatarPermissions.cs

@@ -0,0 +1,7 @@
+namespace FSO.Common.Security
+{
+    public enum AvatarPermissions
+    {
+        WRITE
+    }
+}

server/tso.common/Security/ISecurityContext.cs

@@ -0,0 +1,11 @@
+using System.Collections.Generic;
+
+namespace FSO.Common.Security
+{
+    public interface ISecurityContext
+    {
+        void DemandAvatar(uint id, AvatarPermissions permission);
+        void DemandAvatars(IEnumerable<uint> id, AvatarPermissions permission);
+        void DemandInternalSystem();
+    }
+}

server/tso.common/Security/NullSecurityContext.cs

@@ -0,0 +1,22 @@
+using System.Collections.Generic;
+
+namespace FSO.Common.Security
+{
+    public class NullSecurityContext : ISecurityContext
+    {
+        public static NullSecurityContext INSTANCE = new NullSecurityContext();
+
+
+        public void DemandAvatar(uint id, AvatarPermissions permission)
+        {
+        }
+
+        public void DemandAvatars(IEnumerable<uint> id, AvatarPermissions permission)
+        {
+        }
+
+        public void DemandInternalSystem()
+        {
+        }
+    }
+}