TRUNK-4208: Removed gender as a requirement during PersonValidation, added it instead to PatientValidation.

- Moved unit tests from PersonValidatorTest to PatientValidatorTest to reflect this new behaviour.
TRUNK-4208: Refactored PersonValidator. Extracted birth date validation into it's own method.
TRUNK-4208: Added BirthDate as a required field for Patients.

- Previously this was not a required field
- Added unit tests to check for the newbehaviour.
- Updated existing tests to set birth date on Patients as it's a requirement now.