Move Google analytics script into app script

[mgwalker]

Currently the Google analytics script is the only inline script in our app, and that's causing our Mozilla Observatory score to be a B instead of an A. It's a minor thing, but we can fix it!

This task is done when...

• the Google analytics bootstrap code is moved from index.html to app.js (this will also remove it from dev, which is probably a good thing)
• after the new app.js is deployed to production, AWS is updated
• the staging and production Lambda functions are updated to remove inline-unsafe from the script-src section of the Content-Security-Policy header
• new versions of the staging and production functions are deployed
• the staging and production CloudFront distributions are updated with the new Lambda functions' ARNs (CloudFront -> Edit distribution -> Behaviors -> update each existing behavior)