Traffic ground status (defaulted to hide display/silence alerts) and speed filters

Per Avare Github issue #371, I propagated the airborne ADSB flag up to the traffic object, and also saved the same flag for ownship into the traffic cache. I then used these newly propagated flags to add configuration options for both visual and audible traffic display/alerts (both defaulted to hide the ground traffic). In addition, I also added for the audible alerts the option of a minimum speed under which audible alerts are not played (defaulted to "0", which essentially means the feature/config is disabled by default), to allow for the option of effectively disabling the audible alerts completely during low-speed, high workload times like takeoff and landing--when the aircraft would be airborne, but perhaps during times when the pollution of the audible alerts would be competing with more relevant audible feedback (e.g., GPWS or radio communication).

I also did a fair amount of audible alerts codebase cleanup and decomposition since my initial audible PR--sorry if that presents a little clutter vs. being able to read only the new filter items. To make review somewhat more manageable, I checked in the changes in 3 commits: 1.) the addition/propagation of the "isairborne" flag up to the traffic and cache objects and the view config setting (defaulted to be hiding ground traffic now); 2.) the use of those flags by the audible alerts, also defaulted to hide ground traffic, whether it is the ownship or traffic that is on the ground (this commit also does include the refactorings since my initial audible PR); and 3.) the new audible min speed filter (defaulted to 0 knots Vh/disabled).

apps4av / avare

Traffic ground status (defaulted to hide display/silence alerts) and speed filters #480