Customize map markers and popups

[gregjd]

Markers need WWC vs. non-WWC, which will require importing data from the existing GeoJSON. (Also that GeoJSON can give us the dates.)

Number of policies:

• If zero policies: don't display marker
• If one policy: display year, means, link to policy page
• If multiple policies: display number of policies (possibly year of most recent), link to place page

[gregjd]

Update: 9ca2390 addresses the "number of policies" issue. I changed it so that it will just show a list of all policies for that place. So, basically the "if one policy" solution but for all policies, sorted in reverse chronological order.

Haven't yet explicitly handled the case where a place has no policies (which would happen if a place was added to _places but didn't actually have any associated documents).