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).
Actually this method is named wrongly, it is calculating nothing, it is just returning an effective activation date based on the urgency, i would rename it getEffectiveActivationDate()