Trunk-4444 Validate order overlap with scheduled date

Comments:
In Order.java:
          - getCalculatedStartDate and getCalculatedEndDate are kept public for future use.
          - Can rename getCalculatedEndDate and getCalculatedStartDate with better names (if any).
I was looking at this and realized something strange, how can order1 have startDate after that of order2 but before the stop date of order 2 still? It would mean order2 must be having awkward dates where the stop date comes before its start date which wouldn't make sense.