issue:     canvas pans when tap on touch screen
issue:
    canvas pans when tap on touch screen

reason:
    onTouchStart calls onMouseDown which registers 'mousemove' event handler.
    when I tap on touch screen, even though browser did not dispatch 'touchmove' event, it dispatched 'mousemove' event.
    therefore, the 'mousemove' handler pans canvas.

fix:
    stop onTouchStart handler registering 'mousemove' handler as onMouseMove will be properly triggered by onTouchMove

jmnetus/openseadragon,shaunstanislaus/openseadragon,shaunstanislaus/openseadragon,mcanthony/openseadragon,sul-dlss/openseadragon,avandecreme/openseadragon,seanich/openseadragon,seanich/openseadragon,LarissaSmith/openseadragon,TMUND/openseadragon,jmnetus/openseadragon,Iced-Tea/openseadragon,openseadragon/openseadragon,janelia-flyem/openseadragon,rdlester/openseadragon,lidasong2014/openseadragon,openseadragon/openseadragon,ricochet2200/openseadragon,LarissaSmith/openseadragon,daverome/openseadragon,msalsbery/openseadragon,rdlester/openseadragon,Iced-Tea/openseadragon,goofwear/openseadragon,avandecreme/openseadragon,janelia-flyem/openseadragon,ricochet2200/openseadragon,lidasong2014/openseadragon,msalsbery/openseadragon,daverome/openseadragon,goofwear/openseadragon,LafayetteCollegeLibraries/openseadragon,mcanthony/openseadragon,TMUND/openseadragon