Added guards to load() and unload()
Now, in alternativeStrategy, the Elevator
checks before loading or unloading a Customer.
With this changes the Elevator does not open
the doors if not needed.
The efficiency counter therefore needed to be
reengineered to calculate the times the Elevator
opened its doors.
Merge pull request #27 from asasse01/refactor_alternative_strategy

Added guards to load() and unload()