Wire up Organization in other data types

Summary:
Use the newly-made class as provider in Reservation, Flight,
TrainTrip and BusTrip

Test Plan: Added unit test, passed

Reviewers: vkrause

Reviewed By: vkrause

Subscribers: KDE PIM, vkrause

Tags: KDE PIM

Differential Revision: https://phabricator.kde.org/D11935