Pass requested data to extension internally

Since the extension only gets the parsed POST data from the [server.py](https://github.com/yillkid/iota-swarm-node/blob/1698cd5f7783f526dfe00d7a73c4a49420307c57/server.py#L63), it would be nice to let extension get the raw data, HTTP Header and `request_path`, it will give the extension more ability. 🤔 