DaylightUI's add method now asserts if the hour count exceeds the max
hours. This shouldn't ever be able to happen. DaylightUI's subtract method
now does the subtraction and if the hour count goes below the allowable
minimum the subtraction is ignored and false is returned. BarrelNode,
ClinicNode, DoorNode, HouseNode, and WindowNode now check the return from
the subtract method and act accordingly.