Implement NetworkManager

For now there are two methods:

- `NETWORK:IsUrlAllowed()`: Check whether access to a certain URL is allowed.
- `NETWORK:HttpRequest()`: Perform an HTTP request.

By default access to the network is disabled for all target hosts. It
can be enabled by setting `HttpEnable=1` in the preferences. Individual
hosts have to be added to `HttpAllowHosts` as a comma separated list to
allow access.

See included docs for more details on usage.

extern/IXWebSocket-11.3.2/test/compatibility/python/websockets/Procfile

@@ -0,0 +1,3 @@
+nginx: nginx -p . -c nginx.conf
+websocket_server: python echo_server.py
+send: sleep 1 ; ws send -x --verify_none wss://localhost:8765 /usr/local/bin/ws