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/entrypoint.sh

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+case $MODE in
+    echo_server)
+        python /usr/bin/echo_server.py
+        ;;
+    echo_server_ssl)
+        python /usr/bin/echo_server_ssl.py
+        ;;
+    broadcast_server)
+        python /usr/bin/broadcast_server.py
+        ;;
+    broadcast_server_ssl)
+        python /usr/bin/broadcast_server_ssl.py
+        ;;
+esac