Allow inclusion of 6 months of data in heatmap

* Heatmap will be more accurate/useful with more data
* Fetch and use past 6 months of data for heatmap
* Reflect time period and count in heatmap legend
* Allow API query to start in June
Oh, and it's a little over 6 months ago. I changed it from a year ago b/c I had such geocoding issues yesterday and it will be easier if I'm trying to grab less data. The point is to grab data from at least the last 6 months, if possible, so that I can show 6 months of data on the heatmap.