Multiple fixes for iOS Safari

In iOS Safari bxslider freezes when a slide is swiped (horizontally) immediately after interacting with slide controls (pager or slide buttons). It also freezes when a horizonal swipe also causes page to scroll in vertical direction such as when finger moves up or down after touching the slide and then moves to left or right to swipe the slide. This pull request fixes both issues by disabling slider controls during a swipe and using setTimeout to avoid iOS Safari's touchend handler block firing of transitionend event. Also slider controls' click handler now is set to fire on "touchend" to avoid the well-known 300ms click delay on touch devices.