By Michael Holden and William James LONDON (Reuters) – Britain imposed sanctions on Chelsea soccer club owner Roman Abramovich and Igor Sechin, chief executive of Russian oil giant Rosneft, hitting them with asset freezes and travel bans because of their links to Russian President Vladimir Putin. The two billionaires plus Oleg Deripaska and four other Russian oligarchs are the most high-profile tycoons to be added to the British sanctions list since Russia invaded Ukraine. The move follows criticism that Britain has been acting too slowly. The action puts on ice Abramovich’s plans to sell Prem…