Draft: Popularity Contest

This is the first stab at a "popularity contest" following Debian's model. The goal is to collect useful information about F-Droid usage without collecting any Personally Identifing Information (PII). This should also avoid collecting information that can lead to deanonymization, when possible. Guaranteeing that will be basically impossible.

This is part of the @cleaninsights project, which is a Guardian Project project, and it will probably be implemented using the https://gitlab.com/cleaninsights/clean-insights-android-sdk to report data to the Clean Insights Matomo server. That server has a pre-processor to strip out PII that might have mistakenly made it to the submission process.

This has been thoroughly discussed at #396 (closed), I also welcome feedback now.

@uniqx @IzzySoft @TheLastProject @sorenstoutner @k3b @danuker @CiaranG