MaterialPreviewRenderer: set proper GL z and matrix state instead of relying on previously set values.
Visualize light source, transform light into viewspace.
Also update fixheaders.py script with new copyright info template.
Improve light rotation.
Add RunOnceGuard utility to make sure only one (visible) open3mod instance is active at a time, and further instances dispatch to it.
Fix bug that caused light direction in the first viewport being drawn to be wrong.
FPSCamera: fix rotation axis for y mouse deltas.
FPSCamera: further fixes, now behaves as expected.