Command fixes

Controls:
-only allows right click commanding when plane is commandable

Flight:
-only matches runway waypoints when altitude == 0
-fixed landing logic to ignore multiple land requests
-provide isCommandable() value to command issuers

FlightMenu:
-only allow non-take-off/landing commands when plane is commandable
-only draw speed/altitude markers when within constraints
-double version of constrain() provided to prevent irrelevant roundind
-fixed to disable commands as well as rendering when not commandable