Fix #184 : move from app.php to NC 20 Application.php

[smarinier]

• use NC 20 api
• modify required NC version to 20

[mkrecek234]

@ACTom Hi, could you PLEASE check the PR and merge it if possible? We desperately need a proper version which does not throw endless debug errors. Otherweise we need to fork the project and list the fork at Nextcloud to be sured it stays maintained. Your mindmap is really awesome, we just need to stay a bit more up to date ;-)

[mkrecek234]

@ACTom Thanks a lot - and if we could get a new version released, so Nextcloud is showing an update. Thank you very much. Your app is very essential to me and others

[ACTom]

I'm in the process of testing the versions for compatibility and will release a new version as soon as I'm done.