Beginning to understand radar state report
Report received commands from other control heads.

A separate thread now monitors what other control heads send for commands.
Going in the direction where verbose logging is going to be all we need to
do future reverse engineering of the still missing controls, without needing
tcpdump.
Fix scan age calculation to be time based.

When you scroll or move the image the rendering code can be called many times a second.
This causes the radar image to be removed as the 'age' calculation depended on the
renderer being called every second. This has now been changed to a date based
algorithm, so it is no longer dependent on that.

Also lock the data structure whilst drawing + changing, this does not seem to make
a huge difference but at least it is safer.