How about add "dragmove" api event?

[dbwodlf3]

pannellum can dragmove change viewport, but there aren't some api event.

https://github.com/mpetroff/pannellum/blob/master/src/js/pannellum.js#L872

    if (draggingHotSpot) {
        moveHotSpot(draggingHotSpot, event);
        fireEvent("dragmove");
    } ...

I would like to hook moveHotspot function.