PowhegControl Parameter changes, and bb4l SL fixes

This MR introduces:

• new parameter whichW for semilep bb4l
• renamed two parameters use_OLP_Interface ttJ and ttJ_MiNNLO
• width_correction->widthCorrection
• twidth_phsphas now by default the same value as twidth
• changed the way semilep bb4l executable is called during event generation