Add methods to check if widgets are currently shown/expanded/visible or not

Created by: bitcity

I'm surprised there's no request for a function that tells if a tooltip (or popover) is visible or maybe I missed it in the issues. The closest I could find was this on Stackoverflow (these are workarounds and could break unexpectedly in a future update).

How about something like:

  Tooltip.prototype.isVisible = function (obj) {
    var self = ...
    if (self && self.$tip && self.$tip.is(':visible')) {
      return true;
    } else {
      return false;
    }

I understand that it isn't completely deterministic since the result could change due to an animation timeout or mouse event.