Workers’ compensation — Compensable injuries — Evidence — Expert opinion — Judge of compensation claims erred in admitting opinion of claimant’s independent medical examiner that exposure to mold in the workplace was the major contributing cause of claimant’s injury where opinion was based on improper bolstering and lacked a sufficient factual foundation — Expert opinion was improperly bolstered by professional opinions and reports of others and by inadmissible medical records of claimant’s co-worker