Migrate Android Realm data on first app startup

[shockbytes]

Extract the potential data from the old Android App and push it to Firebase, then mark the Realm data as migrated and keep it untouched.

https://pub.dev/packages/realm

[lockieRichter]

@shockbytes can you elaborate a bit more on what you are thinking for this ticket?

[shockbytes]

Right now, all data is stored in Realm for the Android app. We need to work on a migration scenario, where we extract the already stored data from the app version 4.x and migrate the data to Firebase at first app open. Hence, we need to add the realm dependency, grab all data and push to Firebase.

I will assign myself to this ticket, as this is the highest priority for me right now. I am confident that we can make this work easily, but this ticket is crucial for DanteX. If this does not work, we are in quite a bad place :D