Add synchronization step to IQ pipeline

[rocapal]

In order to synchronize several receivers for sensing and retrieving IQ data is needed to add a synchronization step in order to start the sampling at the same time.

1. Assuming that the receivers are synchronized using NTP.
2. Controller will send the same absolute time to the sensors.
3. Sensors will run the process, open the SDR and get ready for sampling.
4. When the absolute time arrives (defined in step 2) the sampling process will start.