“A member of the Bar is not entitled to refuse his services to anyone who seeks to employ him. He has been said to be like a cabman on the rank: it is his duty to place himself at the disposal of the first person who hails him and he has no right to exercise any discrimination... This principle also has its origin in the conception of the special position of the advocate in the public administration of justice. It is essential that no citizen should be unable to procure the adequate presentation of his case in Court, however unpopular or even unworthy he may be.”