Adds an option to mouse-pan the HiPS graphics.

Summary:
Previous while panning (holding the mouse button down and moving the mouse) the HiPS overlay would not redraw
until the mouse was released. This adds a checkbox option for smooth panning with HiPS displayed, if the
option is checked. I have left the default false for now.

Reviewers: mutlaqja

Reviewed By: mutlaqja

Subscribers: kde-edu

Tags: KDE Edu

Differential Revision: https://phabricator.kde.org/D24605