Improve Responsive/Mobile/Touch friendliness of slider plugin

To elaborate on user experience: The slider images distort rather than resizing until you get to the next breakpoint. It would seem the height is being defined, whereas it needs to remain undefined so it adapts.

Seems like the "getimagesize" function is looking for both dimensions, which it shouldn't if it's going to be adaptive. You only want to define the width and let the height adapt.