Next app architecture steps

[tobiasKaminsky]

Since the last days I read a lot on how to improve the app on a more deeper level.
So here are my rough ideas, which can and should be discussed.

I will list them as an overview and then open new issues to get in more detailed discussion.

• switch to modern system
• switch to WorkManager
• use Lombok
• use dav4android, with okhttp3
• hard seperation of client / library

[strugee]

I've checked the "switch to WorkManager" box since that ticket got closed - feel free to undo if that's incorrect