[ical4j 4.x] Test with all known test accounts

[rfc2822]

See https://github.com/bitfireAT/davx5/wiki/test-accounts

Idea: If there are others on https://www.davx5.com/tested-with/, but we don't have test accounts, maybe its worth to create a test account (if possible) and add to test-accounts.

What to check for each server

• Add events on server, sync down to DAVx5
• Add events in DAVx5, sync up to server

Especially have a look at timezones, so for instance when creating events, use different timezones and see whether they sync correctly.

Also use recurring events and exceptions of them.

If the server supports tasks:

• Add tasks on server, sync down to DAVx5
• Add tasks in DAVx5, sync up to server

Important

Take notes of all problems in the respective issue and if it could be a synctools/DAVx5 problem, create a separate issue referencing the "test with" issue.

For better task board clarity I suggest that we don't add every subitem / service to the sprint backlog / task board (but nevertheless use assign and close etc.)