Enforce is_primary field at db or dao level

Currently is_primary is enforced at the form layer, but this is not 100% reliable and doesn't help at all from the API layer, etc.

Desired behavior:
1. When creating, updating, or deleting an entity with an is_primary field, ensure that one and only one record of this type per parent object contains is_primary = 1. In the case of deleting the primary, we will just have to pick another at random and assign it as primary.

2. Find a clever way to automagically attach this behavior to any field in the db named is_primary so we are not creating and maintaining special cases for email, phone, address and any entities added in future.