XNAT-3024: Null values in some fields were breaking the PET archive page
XNAT-3313: Fixed bad logic for determining when REST call was made just to update status.
XNAT-3271: It looks like this bug was actually fixed previously.  But, while in the code, I added another check to prevent scans from being created using the abstract type 'xnat:imageScanData'.
XNAT-3189: Modify Custom User group to prevent display name duplication attempts.
XNAT-3276: Added various permissions checks for each REST call.
XNAT-3317 Made file generic for imageAssessor datatype.