Add analytics events to various things in app

[jordansread]

Best example so far is in climate-change-walleye-bass viz

[wdwatkins]

Thinking events to start:

• toggling on/off each use category on the map
• moving the slider to each timestep
• which state was moused over, for which period and category
• which exit links were clicked

[eread-usgs]

@wdwatkins how is progress on this one going?

[wdwatkins]

should be finished with #156 merged