A dark, quirky British comedy whose cast is led by The Mighty Boosh’s Julian Barrett and Oscar-winner Olivia Colman? You need not twist my arm! But Flowers is not a show that is immediately easy to like, but is a reward for those who stick with it. It initially has the trappings of a classic black comedy — the opening scene is of Barrett’s children’s book author Maurice trying to hang himself and the branch breaking to save him— but as it continues it reveals itself more as a closed-in emotional horror. It is also a …