Navigate with back/forward mouse buttons in panel view to go back/forward in dir history

Summary:
"Back" and "Forward" mouse buttons (aka buttons 4 and 5) are connected to back/forward history commands.

+ Fix small bug that came with e7d8a5df:
Wheel event might have been handled twice.

Test Plan: Tested history navigation, both view types, both panels

Reviewers: Krusader, asensi

Reviewed By: Krusader, asensi

Subscribers: asensi

Differential Revision: https://phabricator.kde.org/D2206