(This February 24 story corrects pounds to dollars in second entry) By Andrew MacAskill LONDON (Reuters) – British Prime Minister Boris Johnson unveiled a package of “severe” sanctions against Russia on Thursday, targeting banks, members of President Vladimir Putin’s closest circle and the extremely wealthy who enjoy high-rolling London lifestyles. Hundreds of billions of dollars have flowed into London and Britain’s overseas territories from Russia since the fall of the Soviet Union in 1991, and London has become the Western city of choice for the super-wealthy of Russia and other former Sovi…