Bike theft layer should be heatmap

[mvl22]

The bike theft layer currently is a live feed from the police API, but has numerous shortcomings:

• Multiple reports in the same place get overlaid, so can't be seen
• Should be a heatmap
• No historical comparison over time

[mvl22]

Heatmap example at:
https://tinyurl.com/yc8a2t23