feat(ui): provide a view that can be overlayed on 3D scenes

Description

These changes add a new OverlayLayoutManager that allows to add overlays to a widget. See the corresponding issue #1089 (closed) for a description of this layout manager. All occurrences of the slideView widget in SightViewer was replaced by an OverlayLayoutManager.

Closes #1089 (closed)

How to test it?

Test the modified applications for any regression: SightViewer (including the PACS window), SightCalibrator and ExDicomSegmentation.

Ideally, we should test with multiple systems and windows managers.