Implement replaying CalDAV events and calendars

Summary:
Notes:

• For calendars, only removal is implemented because:
  • There is no DavCollectionCreateJob, possibly because there can't be an empty DAV collection
  • DavCollectionModifyJob only allows modifying "properties", which we don't use (except for the name, if the name is considered a property)
• Currently, modifying an item with Sink overrides the one on the server, even if the store is not up-to-date

Reviewers: cmollekopf

Tags: Sink

Differential Revision: https://phabricator.kde.org/D12611