Migrator: implement Google Resource migrator

Summary:
Implement a migrator that migrates the user from the legacy Google Calendar
and Google Contacts resources to the new unified Google Groupware Resource.

Reviewers: poboiko, vkrause

Reviewed By: poboiko

Subscribers: kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D28957