issue cannot enroll patient in a program more than once TRUNK-3483 and 4322 solution
changes done as per comment made in the pull request
added empty option to the selection list
TRUNK-4031: locking mechanism for patient_identifier_type
Merge pull request #935 from harsha89/TRUNK-4314-add

added empty option to the selection list TRUNK-4314
Merge pull request #937 from rpuzdrowski/TRUNK-4031

TRUNK-4031: locking mechanism for patient_identifier_type
Merge pull request #930 from harsha89/TRUNK-3483_4322

issue cannot enroll patient in a program more than once TRUNK-3483 and 4322 solution