The Olympia Theatre quickly fills up as Slow Skies take to the stage as tonight’s warm-up for the impending spectacle of St Vincent. Possibly to make the latter’s immaculate stage set up possible, the former are down to headcount of three, and squeezed to the front of the stage. With the reduced set up, all the pressure is on the delicately soaring voice of Karen Sheridan (below) to carry them into the attention of the waiting crowd. After a slightly nervous start, she settles into the new surroundings and by the time they swell into on the shore (the lead…