TODO: Remove Realm support and legacy migrations

Currently the APK size is huge (17 MB) for what the app contains. This is due to native binaries for the Realm database being included. v3 no longer uses Realm (switched to Room) as database. Realm is still included so users can migrate easier. In a future version, after some time has passed, we should remove Realm and any migration code. This should reduce APK size by ~ 10MB. Future users will just have to setup the app again or first install an older version. Let's say in 4-6 months? After Google Play shows 80%+ on a v3 build 🤔