Massive Cleanup of asgn2Vehicles

Changed some private parameters to protected to allow them to be used in
subclasses.
Deleted subclass parameters, use base vehicle parameters.
Added throws (or I did this last submission)
Added comments.

Fixed contructors of subclasses breaking: apparently a default
constructor for the superclass was required.
Deleted intendedDuration: unused

Only thing to do in asgn2Vehicles: toString function