Easy connect

all changes are related to the PROPFIND request / response.
now it is possible to connect and retrieve your collections by
1. request your current-user-principal or principal-URL from any URL / path
2. request your calendar/addressbook-home-set from the principal URL
3. perform a PROPFIND with depth = 1 on the "*-home-set" URL to get all your collections

the specs taken from [rfc4791](http://tools.ietf.org/html/rfc4791) and [rfc5397](http://tools.ietf.org/html/rfc5397.html).

this fixes are required to get the firefox-os calendar app working.