validation: move Controller::Ajax methods to LIMS::Validation

take request_id/error_code_id UK off request_error_code to allow multiple entries
add error_code for each entry in hilis3.Log & request & patient_case edit in hilis4
add error codes to history view

fixed relationship omissons in M::Worklist causing template loops to request db lookups

globally-available 'new clinician' link target in registration section requires admin permissions