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/Rendering/Framework/IO/IFocusableUI.cs

@@ -0,0 +1,13 @@
+namespace FSO.Common.Rendering.Framework.IO
+{
+    public interface IFocusableUI
+    {
+        void OnFocusChanged(FocusEvent newFocus);
+    }
+
+    public enum FocusEvent
+    {
+        FocusIn,
+        FocusOut
+    }
+}