Revert touch devices tooltips disabling and fix double taps on iOS

[jonathanarbely]

trafficstars

The culprit (src):

//if it is a touch device, hide hovering tooltip
if (opt.isTouchDevice) opt.hoveringTooltip = false;

I can only see one reason for this line of code, which is to prevent the double tap issue on iOS. Other then that, why hide important info delivered through the tooltips? This significantly reduces UX.

If we can't figure out a good reason for this, I'd propose a PR (in which I'll also try fixing the iOS double tap issue).

[monovertex]

This has been also mentioned in #147 and #467. I'm keeping this issue open to track this problem. PRs are welcome!