Improve service discovery

[DanielPollithy]

Use the WiFi P2P service API or at least use UDP broadcast

[DanielPollithy]

A better option would be to start a WiFi-Hotspot with a given name "IotWifi-xxxx". That could replace the shaky wifi p2p which has the following problems:

• WPS necessary (user interaction)
• not all devices can be group owners etc.