Resource sharing feature is incomplete

[alecpl]

I started implementing draft-pot-webdav-resource-sharing in my client. And the state of things in cyrus does not look great regarding this. Here's some points to consider.

• Cyrus implements v2 of the standard, while v3 and v4 exists and is quite different.
• Because resourcetype property is not implemented there's no way a sharee can know whether a shared collection is an addressbook or calendar (you'd have to make a guess based on the hosturl property).
• Because displayname is not implemented I don't see the proper name of a collection. I have to derive it from hosturl, which may contain an uuid instead of what a displayname would contain.
• There's no way (including v4 of the standard) to know whether a calendar collection accepts VTODO or not. I'd like to see supported-calendar-component-set property in the invite XML.

EDIT: Actually supported-calendar-component-set exist on calendar folders, so we can recognize the type.