Touch Support

[Sudrien]

Trying version 1.17.1 on Firefox Nightly

Looking though code, _box.addEventListener('mouseover', ...) is working - I get a download icon

But _btn.addEventListener('click', ...) is not working, as I never get a download prompt.

Looking through https://developer.mozilla.org/en-US/docs/Web/API/Touch_events, I think a touchend event handler is also needed.