Added support for WebSocket transport on MQTT client

[tcalmant]

• Added support for ws:// and wss:// protocols
• Added a path MQTT client configuration option, used only with WebSocket protocol
• Automatic switch to wss:// when using ws:// and client authentication
• Added tests to ensure WebSocket connectivity works
• Fixed NPE on reconnect
• Upgraded to Moquette 0.17

Sample MQTT client configuration:

{
  "id": "handlerWS",
  "protocol": "ws",
  "host": "mqtt-broker",
  "port": 9001,
  "path": "/mqtt-ws",
  "topics": ["sensor/#"]
}

Fixes #235