Import UriHandler code from KdepimDBusInterfaces

Summary:
The code has been largely adapted and improved to better handle all URLs
and to not rely on DBus interfaces and/or directly linking against some
other PIM libraries. Instead, invocation happens through
KRun using the "view" services of KMail, KAddressbook and KOrganizer.

The code is used by calendaring apps to handle opening links to attachments.

Reviewers: #kde_pim, winterz

Reviewed By: #kde_pim, winterz

Subscribers: winterz, kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D29543