Add enum_Unknown; update definition of Family ID; clarify Parent and Collection Sample policy

[lopierra]

• Changed Age ranges from numeric to numeric OR Unknown, since some studies (e.g. X01-Hakonarson) did not collect ages for all participants
• Updated definition of Family ID to specify not required for Proband-only individuals
• Clarify that Parent and Collection info is required for each Sample, and that each Parent and Collection must also be listed as a Sample