mousewheel deltaFactor

Upgrades the mousewheel plugin to 3.1.6 and uses the new event.deltaFactor property. If the event.deltaFactor does not exist, because an older mousewheel plugin is being used, it will fallback to the mouseWheelSpeed setting. This should provide a more tailored user experience because the browser is reporting the distance in pixels the content should scroll based on the users browser, os, device, and settings.