Discovery of N(3-Carbamoyl-5,5,7,7-Tetramethyl-5,7-Dihydro4Hthieno[2,3c]pyran-2-Yl)lHpyrazole-5-Carboxamide (GLPG1837), a Novel Potentiator Which Can Open Class III Mutant Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Channels to a High Extent