added _missingSequenceNumbers tracking to OctreeInboundPacketProcessor
added code for AC to send nack packets; no locking yet
added locking on _singleSenderStats; untested!
Revert "added locking on _singleSenderStats; untested!"

This reverts commit c542da97076ba0d27f4e191ae5d8249dbf8afe7e.
Revert "added code for AC to send nack packets; no locking yet"

This reverts commit 15bd0878c407ede95f724009adadc81deeb7b4fd.
rollovers are now handled in SingleSenderStats::trackInboundPacket
Working on JSON encoding.
More work on JSON encoding.
I think that basically covers the JSON writing portion.
Spoke a little too soon.
Starting to work on JSON reading.
added sendNackPackets() to OctreeInboundPacketProcessor

added rollover handling in _missingSequenceNumbers pruning; added
EditNack packet types; added getMyEditNackType() to OctreeServer
subclasses; added code to randomly skip edit packet sequence numbers for
testing in OctreeEditPacketSender
added OctreeInboundPacketProcessor::process() override to send nack periodically

added code to remove dead nodes' stats in sendNackPackets()
minor changes before moving SentPacketHistory
moved SentPacketHistory to libraries/networking/src
removed old SentPacketHistory
More progress on json reading.
added code to parse nack packets in OctreeEditPacketSender
SentPacketHistory now handles rollover

updated SentPacketHistory path in comments
removed magic number 65536 from OctreeInboundPacketProcessor