Add Shortcut to zoom to bounding box of _layerGroup

[nsubordin81]

It would be nice to have a flag or some other type of configurable option that you could pass in when instantiating the leaflet object that would listen for a crossfilter filter event or append to the redraw event and it would fit the bounds of the internally managed map to the layer group. The easiest way for me to add this in my own code was to just always do it in the redraw method of my local dc.leaflet.js, but it is not an elegant solution:

  _chart._doRedraw = function () {
//doRedraw function body. . . 
  if (_chart.cluster() && addList.length > 0) {
      _layerGroup.addLayers(addList);
    }
  //this is where the redraw function usually ends

  //create a featureGroup from the layers in the layer group so we can call .getBounds()
    var _boundFeatures = L.featureGroup(_layerGroup.getLayers());
  //the usual method for fitting the bounding box around the markers
    _chart.map().fitBounds(_boundFeatures.getBounds());
  }; //end doRedraw()