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/ws_send.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+
+# websocket send client
+
+import argparse
+import asyncio
+import websockets
+
+
+async def send(url, path):
+    async with websockets.connect(url, ping_timeout=None, ping_interval=None) as ws:
+        with open(path, 'rb') as f:
+            message = f.read()
+
+        print('Sending message...')
+        await ws.send(message)
+        print('Message sent.')
+
+
+if __name__ == '__main__':
+    parser = argparse.ArgumentParser(description='websocket proxy.')
+    parser.add_argument('--path', help='Path to the file to send.',
+                        default='small_file')
+    parser.add_argument('--url', help='Remote websocket url',
+                        default='wss://echo.websocket.org')
+    args = parser.parse_args()
+
+    asyncio.get_event_loop().run_until_complete(send(args.url, args.path))