Tracker firmware: Test what happens when backend is restarted

[saerdnaer]

During the last days we had one time an issue with the server, which led to it being restarted. The trackers were not able to send data to the new instance anymore, we actually had to power cycle them. It looks like the http library was dead locked...

TODO: Deploy the refactored firmware (see PR #41) or use
https://gist.github.com/saerdnaer/048b7abc0698c3671a0baf312bbfffa3 to a tracker, while connecting it via usb serial, restart the server and see what the tracker does aka what the error responses are.