Refactored filterLegend to reset visible buildings upon click
Refactored filterLegend to reset visible buildings upon click

Previously a click would add a filter to the legend, but not reset the
visible buildings.  As a result, clicking on two different legend items
would totally clear all markers from the map.

codefordenver/denver-sustainability,codefordenver/denver-sustainability,codefordenver/denver-sustainability,codefordenver/denver-sustainability