Concurrent API calls and measurements

[danieltsoukup]

Issue
At the moment, when the sensor is sending measurements to the database, there are no noise measurements made which results in missing a few seconds of data.

Proposal
Explore options to make sure that the noise measurements do not stop while previous values are sent to the database.

[tcsullivan]

The sensor firmware runs on top of a real-time operating system, FreeRTOS, which supports multi-threaded execution. I would propose having two threads, one that runs the decibel sampling and another which runs API calls every five minutes.

Some synchronization will be needed for the list of DataPackets that are ready for upload.

[tcsullivan]

The noise measurements should start as soon as possible too, no need to wait for the WiFi to connect. Of course, don't start the measurements if the device is unregistered (and may not be properly positioned then?).