Expose integer primary keys to all resources

At present, the RESTAPI is based on UUIDs. This causes two problems:

1. The packet size increases considerably. For example, an observation REASON OF SAMPLE REJECTION = SALIVA will be transported as: 

   {"126224AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA":"160013AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"}

   this can easily be transported as: 

   {126224:160013}

1. Some validations aren't possible on client-end. For example, if a person attribute type MARITAL STATUS can only allow a set of concepts SINGLE, MARRIED, etc. then while defining this person attribute type, the integer concept ID is saved as foreign key, not the UUID (check the screenshot)

I'm not sure the downsides of this. It will be better to explain thoroughly in case this request is turned down.