Put the following files from your dedicated server in this folder:
- 0Harmony.dll
- Assembly-CSharp.dll
- Assembly-CSharp-firstpass.dll
- com.rlabrecque.steamworks.net.dll
- LogLibrary.dll
- mscorlib.dll
- System.dll
- System.Xml.dll
- System.Xml.Linq.dll
- UnityEngine.CoreModule.dll
- UnityEngine.dll 
- UnityEngine.ImageConversionModule.dll
- Utf8Json.dll

Also, grab the following two from the "vanilla web mods":
- MapRendering.dll
- WebServer.dll
