Fix scene midpoint detection.
MaterialPreviewRenderer: always set depthmask=true, this fixes a visibility problem with some transparent materials.
Further simplify code to compute scene bounds.
#Fix Scale in TimeSlider

switched to an adapting scale
+Add dirty flat to OrbitCamera

to save matrix multiplications
#Fix Splitter Bug causing overlapping viewports

Cleanup Splitter and Viewport Bounds Infrastructure
#Fix default position of separators
Add ICameraController.SetPivot() and implement it for OrbitCameraController s.t. the scene orbits around the geometric center of the scene.
OrbitCameraController: SetPivot() now uses dirty flag.
Comment test code.
Updated to latest assimp-net version.
Improve logging formatting.
Heuristically ignore all-black diffuse material color on textured surfaces.
First draft of pivoting feature.
OrbitCameraController: revert pitch for mouse input to fix weird pitching.
Further work on pivoting feature, it now takes the center of the selected node.
Fix pivot computation.
Fix unintended assertions.
Highlight pivot in hierarchy view.