Update v5.5.5 & v5.5.6 — Endless ATC Steam update #859603

Minor adjustments and bug fixes in v5.5.5 (4 April): Fixed issue where planes inbound secondary airports could not land after a go-around in case the runway configuration had changed to a takeoff-only config. For example, planes inbound RD airport may now change destination to EHAM after going around. Blue plane messages now remain visible after a runway configuration change. Slightly reduced the climb rate of planes just after takeoff. For custom airports, adjustments to the transition altitude/lowest flight level at USA airports, to make it closer to reality: 'transitionaltitude=18000' will now be interpreted as 17000 to make FL180 available at high pressures, as it is in real life. The lowest selectable FL will not drop below FL180. And the lowest FL will now increase in steps of 10 instead of 5 (for example FL190 instead of FL185). These adjustments only affect 'usa=true' airports wi...