enh(ui): use Qt layout instead of multiple 3D viewports in SightViewer

Description

These changes replace the usage of multiple 3D viewports in SightViewer with Qt layouts and multiple 3D scenes. The single scene "genericSceneSrv" is replaced with 4 scenes "mainSceneSrv", "axialSceneSrv", "sagittalSceneSrv" and "frontalSceneSrv", organized in two LineLayoutManager to make a grid. All instances of SViewportUpdater have been removed, as the layouts will do the resizing.

While this new version works, some flickering may be seen when passing from the volume view (with only the main scene) to the negato view (with the four scenes) and vice versa.

Closes #982 (closed)

How to test it?

Launch SightViewer, load an image, and check if it works both in the volume view and in the negato view and that there are no regressions.