store name of VisB JSON file

Signed-off-by: Michael Leuschel <leuschel@uni-duesseldorf.de>

B2Program/LandingGear/GearsDoors/LandingGear_R6.mch

 MACHINE LandingGear_R6
+DEFINITIONS
+  VISB_JSON_FILE == "LandingGear_GearsDoors.json"
 SETS /* enumerated */
   DOOR_STATE={open,closed,door_moving};
   GEAR_STATE={retracted,extended,gear_moving};