MIT: record clicks on Facebook and Twitter buttons

These need to be recorded both in Google Analytics (as an
event, using hitCallback, and in our experiments_events
table.
MIT: Make requested changes to the county performance page copy

These were requested in issue #1307
MIT: Make opportunity / threat text green & bold

This was also requested in issue #1307
MIT: use Google Analytics to choose the page variant
MIT: Add the link to the qualtrics survey
MIT: also track clicks on the survey with GA
MIT: also track survey clicks with the experiments app
MIT: record an event for viewing the page in the experiments app