Refactor geostreaming explore view

[ka7eh]

Upgrade the explore view to use the new versions of React and OpenLayers.

This covers two issues originally mentioned here:
https://opensource.ncsa.illinois.edu/jira/browse/GEOD-1367
https://opensource.ncsa.illinois.edu/jira/browse/GEOD-1368

The second issue is about some map interaction stuff. Here's its description:

The map extent should only change when users select a sensor from the sidebar or click on the extent button on the map. In all other scenarios, the extent should not change by user actions. Here are some examples that shouldn't change the extent:

Clicking on a sensor on the map
Closing a sensor popup
Closing a sensor detail view
Toggling any layer
Deselecting a sensor from the sidebar
Toggling clusters

Also, make cluster toggle a configurable option.