/// <summary>
 /// Removes a single bill from the CashDesk object.
 /// </summary>
 /// <param name="singleBill">Bill to remove.</param>
 public void RemoveMoney(Bill singleBill)
 {
     // If bill exists, removes it from CashDesk
     if (this.bills.Keys.Contains(singleBill.Value))
     {
         this.bills.Remove(singleBill.Value);
         this.BillTotalProp -= singleBill.Value;
         Console.WriteLine("SUCCES: removed {0} bill !", singleBill.ToString());
     }
     else
     {
         Console.WriteLine("ERROR: bills list does not contain a {0} bill !", singleBill.ToString());
     }
 }