AfTERGLOW   ✩✩✩✩  Southwark Playhouse, London   It’s Wednesday, Hump Day,  and the irony is not lost on us as the first scene of Afterglow, written and directed by S. Asher Gelman, plunges headfirst down a rabbit hole of naked, balletic grinding. It’s January in London and 0 Celsius outside but the thermostat is turned…