use bus acceleration curve for city bus model (engineering mode)

Generic Vehicles/Engineering Mode/CityBus_AT/Acc_Citybus.vacc

+v [km/h],acc [m/s],dec [m/s]
+0,0.1,-1
+7,1.1,-1
+25,1.1,-1
+50,0.6,-1
+60,0.6,-0.5
+120,0.6,-0.5

Generic Vehicles/Engineering Mode/CityBus_AT/CityBus_AT_PS.vecto

@@ -16,7 +16,7 @@
     "AdvancedAuxiliaryFilePath": "",
     "Aux": [],
     "Padd": 3540.0,
-    "VACC": "Driver.vacc",
+    "VACC": "Acc_Citybus.vacc",
     "StartStop": {
       "Enabled": false,
       "MaxSpeed": 5.0,

Generic Vehicles/Engineering Mode/CityBus_AT/CityBus_AT_Ser.vecto

@@ -16,7 +16,7 @@
     "AdvancedAuxiliaryFilePath": "",
     "Aux": [],
     "Padd": 3540.0,
-    "VACC": "Driver.vacc",
+    "VACC": "Acc_Citybus.vacc",
     "StartStop": {
       "Enabled": false,
       "MaxSpeed": 5.0,