Unit-tests needed

[ncasaril]

This has been moved from Decawave/uwb-core-archive

• lib/uwb_rng - only testing json-encoding and decoding for now
• lib/panmaster, handling of callbacks from lib/pan
• lib/tofdb,
• ... more to come

[ncasaril]

#9 Solves tofdb test requirement.

[szymon-czapracki]

@ncasaril Is there an option to unassign me from this :) (doing some spring cleanups :P )