Update some files to QQC2 and fix minor bug
Summary: The bug was that the Drawer use the drawerOpen properties now instead of just open. Also fix deprecation Kirigami.Label -> QQC2.Label.
Test Plan: Tested on my computer with the touchpad. I could potentialy try with my android phone, if needed.
Subscribers: okular-devel
Tags: Okular
Differential Revision: https://phabricator.kde.org/D18637