Move protocol-related utilities to ProtocolInfo

Summary:
With that there are only two small remaining methods in utils.h, both
unrelated to KDAV as such (and one even unused inside KDAV), so those
can move to the resource and we can get rid of utils.h entirely, and with
it QtXML in the public interface.

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D24291