Add IM protocol information and protocol listing

Summary:
This is largely coming from akonadi-contacts IMProtocol's class, but
adjusted to be more in line with the RFC 4770 format. Non-static methods
for this are to follow.

Reviewers: mlaurent

Reviewed By: mlaurent

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D20705