fixed issue with goodstype validation in part one code, changed != and
== to !str1.equals(str2) and str1.equals(str2) respectively
addCarriage interface working and submitting correctly.

changed FreightCar and PassengerCar show/hide to method

require buttons disabled until loco is added instead of when begin train
is added.

require new button TrainDepart which throws exception if train can't
move - possibly show train weight dynamically and throw exception when
train weight exceeds its pulling power
removed unessary tests to verify goodstype validation was working