option to disable automatic resetActivePageHeight

As I'm increasingly using jQM for "mobile-first, but not mobile only," I'm finding it useful to add a healthy margin around the page for larger screen sizes.  This could be done using only CSS breakpoints were it not for the automated resetActivePageHeight.  This patch allows resetActivePageHeight to function differently above a configurable screen width (like $.mobile.maxTransitionWidth).  Above the specified maxAutoHeightAdjustmentWidth, resetActivePageHeight will clear out the min-height, allowing it to be configured via CSS for larger screen sizes.