Add OemGatewaySocketListener

This allows to use a socket as sample source, as an alternative to the RFM2Pi

Applications:
- other device communicatig through ethernet link
- application located on the Pi itself, sending data through the socket

Data format: '10 20 56\r\n', where 10 is NodeID, 20 and 56 are samples. There
should be 1 to any number of samples.