Add a category for popular and recent events

[stefanmedack]

On https://media.ccc.de/ you can browse 3 main categories: "All Events", "Popular" and "Recent". The conference list displayed on the main page currently covers what you can find on "All Events".

I propose to also add "Popular" and "Recent". Best approach would be to show them like the streaming section with a scrollable list of events.

However, the API of media.ccc.de does not offer this categories. Therefore it would also be important to load all events into the local room database and write queries to extract "Popular" and "Recent". As a little bonus, we could also come up with a "Trending" category. Every category should display a limited amount of events (~20).