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 think it should be fine if one order ends on the date another starts, i don't think that would be an overlap since you could take the last pill of the old medication in the morning and start the new one in the evening of the same day. No so @djazayeri ?