Propagate unused mouse wheel events in edit tools

Summary:
If an edit tool like Crop or Red Eye Reduction is active, zooming
and panning by mouse wheel does not work. This is caused by the
QEvent::accepted flag set to true by default and therefore not
propagating the event.
This patch clears the accepted flag for mouse wheel events until
a subclass of AbstractRasterImageViewTool will accept wheel events
by itself.

FIXED-IN: 18.08.0

Test Plan:

1. Open Gwenview in View Mode
2. Enter Crop or Red Eye Reduction tool
3. Check if Ctrl+wheel zooming works
4. Check if panning with wheel/Alt+wheel works

Reviewers: Gwenview, rkflx

Reviewed By: Gwenview, rkflx

Subscribers: rkflx

Differential Revision: https://phabricator.kde.org/D14286