Ghislaine Maxwell has been mockingly christened “Mary Poppins” by fellow inmates at her cushy new prison due to her cut-glass accent and bizarre obsession with carrying an umbrella. Cons at Federal Prison Camp Bryan in Texas, nicknamed “Club Med” for its relaxed regime and country-club setting, say the disgraced socialite never leaves her cell without her trusty brolly in tow. During the several days in September, the Mirror saw the convicted teen sex trafficker inside the prison, she was