Set Qt::AA_CompressTabletEvents attribute to avoid latency when scrolling with a tablet

Summary:
BUG: 399208

See also: https://bugreports.qt.io/browse/QTBUG-71708

Enabling this option _vastly_ improves the user experience on wacom tablets and touchscreens

Reviewers: Okular

Subscribers: sander, aacid, okular-devel, Okular

Tags: Okular

Differential Revision: https://phabricator.kde.org/D16519