Add Incomplete_Record__c to /Contact GET, PATCH, POST

**Dependencies**
The Coach and Web Registration Apps need to be able to read and write this property on Contact records

**Goals**
As part of support for _Paper Registration_ A Coach may be filling out an incomplete student record in order to begin tracking attendance and then note when a signed registration/waiver is received, to make record keeping accurate. Rules in Salesforce and Apps will manage when these values are set

**Proposed Solution**
Each Method involving Contact identity, demographic, email/phone should also include read/write/update support for Incomplete_Record__c

**Additional context**
This feature is part of https://github.com/AmericaSCORESBayArea/Student-Registration-React-Web/issues/117