Support for Nextcloud 29

[luxzg]

We need to test the app on NC29, and update if needed, or otherwise update app manifest to include latest stable release (max version).

If someone already tested the existing app on NC29 please report the status. If errors occur please post relevant error logs.

Thank you!

Edit Aug 2nd: NC 30 beta was released a week ago, so might as well add that to the to-do as well. If anyone tested NC 30 please report

[brheinfelder]

I'm using Transfer on NC 29 without issue