Add recent earthquakes

[JoshuaCarroll]

The USGS provides an automatically updating KML feed for recent earthquakes at https://earthquake.usgs.gov/earthquakes/feed/v1.0/kml.php. It produces the KML below.

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://www.opengis.net/kml/2.2"><Document><name>Earthquakes</name><visibility>1</visibility><open>1</open><LookAt><longitude>-100</longitude><latitude>39</latitude><range>4000000</range><tilt>0</tilt><heading>0</heading></LookAt><NetworkLink><visibility>1</visibility><refreshVisibility>0</refreshVisibility><open>1</open><name>USGS Magnitude 1.0+ Earthquakes, Past Week</name><Snippet maxLines="1">Updates every 1 minutes</Snippet><Link><href>https://earthquake.usgs.gov/earthquakes/feed/v1.0/summary/1.0_week_age.kml</href><refreshMode>onInterval</refreshMode><refreshInterval>60</refreshInterval></Link></NetworkLink><NetworkLink><name>Tectonic Plates</name><visibility>0</visibility><refreshVisibility>0</refreshVisibility><Link><href>https://earthquake.usgs.gov/learn/plate-boundaries.kmz</href></Link></NetworkLink></Document></kml>

Since this wouldn't need to be used often, I think we should add this as a layer, but it should be off by default.