Local iCal file resources don't provide all rights

Summary:
Turns out our spec was wrong here, we expected to have all rights on the
fallback collection but that's asking a bit too much, some resources
don't provide that. So anything where we can create, change and delete
items only will be good enough. Adjust the spec accordingly.

Reviewers: bensi, franckarrecot

Differential Revision: https://phabricator.kde.org/D703