London band Fat White Family are the bad boys of Britain’s postpunk scene, calling themselves “a drug band with a rock problem.” Even their first album, released in 2013, pushed the boundaries of taste with its title “Champagne Holocaust.” Now comes their fourth album, “Forgiveness Is Yours,” released on April 26. They made headlines when former prime minister Margaret Thatcher died in 2013, showing band members in front of a Brixton pub. Fists raised, they stood by a sheet they painted with the words “The Witch Is Dead!” Frontman Lias Saoudi says “Forgiveness is Yours” is about “life as an et…