Add additional analytics

With https://github.com/developmentseed/co2ordinate/pull/35, we added very basic analytics (page views). This augments Mapbox map load statistics. It would be nice to know a bit more of how the tool is being used, to see its impact and to understand user pain points for future feature prioritization.

Some ideas for additional metadata:

- [ ] Number of users who click on various locations on the map or in the bottom panel (indicating they’re exploring the locations)
- [ ] Number of users who add team members by:
- [ ] Clicking on the map
- [ ] Uploading CSV