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/Content/IContentProvider.cs

@@ -0,0 +1,13 @@
+using System.Collections.Generic;
+
+namespace FSO.Common.Content
+{
+    public interface IContentProvider <T>
+    {
+        T Get(ulong id);
+        T Get(string name);
+        T Get(uint type, uint fileID);
+        T Get(ContentID id);
+        List<IContentReference<T>> List();
+    }
+}