Avoid script errors when changing permissions

* Don't update GDrive permissions for common context roles
* Bail early if the cache is empty
Add UserRole permissions for ProgramAuditOwner

* ProgramAuditOwner needs to be able to delete UserRole assignments when
  changing the Auditor
Add ObjectFolder permissions to ProgramOwner

* ProgramOwners need to create ObjectFolder instances in the Program
  context (when creating Audits)
Merge pull request #962 from reciprocity/feature/fix-program-creator-script-error

Avoid script errors when changing permissions