- startElevator() bug fixes:
   * "==" fixed to .equals().
   * ArrayList copying was done wrong: "ArrayList... = ArrayList..." (copying the reference, instead of making a copy). This has now been removed altogether, as a different approach was used (the "the for loops..." bullet point).
   * "removeCustomer(customerList.get(i)); i--;" has been moved from dropping off a customer to picking up a customer. This is due to the fact that in the "dropping off" bit, the i refers to the registerList, thus the wrong customer ends up being removed.
   * The for loops have been changed to use the real-time value of the relevant variable, rather than a static copy.
   * "if(customerList.size() > 0)" changed to --> "if(customerList.size() > 0 || elevator.getRegisterList().size() > 0)".
- After the above bug fixes, the startElevator() appears to be working 100%, but this requires further testing to verify.