Hide seat reservation section if no seat is reservated

Summary:
On a train without seat reservation hide the section instead of displaying empty forms.

Alternative suggestion: Show "No seats are reserved" message

Test Plan:
Open trip that contains trains with and without seat reservation. Seats are displayed when
available and hidden when not

Reviewers: vkrause

Reviewed By: vkrause

Subscribers: kde-pim

Tags: KDE PIM, KDE Itinerary

Differential Revision: https://phabricator.kde.org/D15352