Introducing iCal delegation setup

Hi Evert,

we would like to use SabreDAV using iCal and we really need to setup delegations from within the client. This feature we implemented now and it works great with iCal 4.0.4, other versions we didn't test yet. To make all informations of a user visible in the user search, while setting up the migration, we also had to introduce an option in Sabre_CalDAV_Principal_Collection to let all users read the information about all other user objects.

In the first step I would ask you, if our changes can have any negative impact, i.e. for security reason, and maybe you are interested in our work and you will merge them into your project.

Greetings from Berlin,
Paul Spieker