A uniqueness check for family external ID on the family form, just like for patient external ID.
This issue does not include checking for uniqueness in REST, controllers, push, etc.
Note: 1.3.5 is added since Gene42 needs this for Addenbrookes who use 1.3.x
_"uniqueuness of family id is something SickKids also wants very soon (based on conversations that @brittney has been having with genetics team)
uniqueness i.e. enforced uniqueness..."_
Currently we are not enforcing patient's externalID. Perhaps we can implement uniqueness check for families and have enforcement of uniqueness as a configurable thing?
As discussed this enforcement will not work on PhenomeCentral, since different institutions may have the same external ID. Does not mean we can't make this an option to be enabled on some instances, but just something to keep in mind