Disambiguation of vanilla use of 'left hand drive'

[originalfoo]

In #580, some TM:PE code was updated to replace confusingly named LeftHandDrive with unambiguous TrafficDrivesOnLeft.

For clarification:

• LHD = left hand driver (so traffic drives on right)
• RHD = right hand driver (so traffic drives on left)
• LHT = left hand traffic (so driver sits on right)
• RHT = right hand traffic (so driver sits on left)

Standard terminology is crazy confusing, hence the rename in #580.

However, there are still issues stemming from vanilla code:

@krzychu124: I will check the code later but vanilla uses that term too. There is LeftHandDrive Vehicle.Flags and LeftHandDrive method in VehicleAI and SnowTruckAI so confusion is inevitable :)

If possible, can we find a way to mask out the crappy vanilla terminology with something better? It will make the code much more comprehensible and maintainable.