Add PlausibleAnalytics Support

[aaronbrethorst]

We'll use AviaryInsights: https://github.com/brightdigit/AviaryInsights

For implementation, I think the Analytics wrapper needs to support sending data to both Google Firebase and Plausible Analytics simultaneously for the time being. In other words, instead of having independent analytics classes, we'll still have the OBAAnalytics class that will manage sending data to both services.