Expose principals as vCards

[helge@…]

CalServer only exposes accounts as principals (aka WebDAV properties), though it adds some contact fields, eg firstname/lastname.

A big issue with the principals in the context of synchronization is that we can't track changes using etags :-/ This more or less prohibits synchronized 'Accounts' folders. (eg we could otherwise expose groups as contact folders and group members as contacts inside those, resource folders etc)

So, it would be *very* helpful, if principal resources would be GETtable vCards, with an etag. A fast hack would do :-) It doesn't need to support full CardDAV (PUT etc), just a minimal vCard representation would be great (just FN/N vCard properties in the simplest case ...).