U2023.12.24-2007: Automatic merge of T1.5.1-791-gffaeec028 and 14 pull requests

- Pull request #570 at 3539862b4: Experimental glTF 2.0 support with PBR lighting
- Pull request #839 at d00beb983: First phase of https://blueprints.launchpad.net/or/+spec/additional-cruise-control-parameters
- Pull request #876 at f92de7665: docs: add source for documents previously on website to source Documentation folder
- Pull request #882 at a055bca64: Blueprint/train car operations UI window
- Pull request #885 at d9ce84bbe: feat: Add notifications to Menu
- Pull request #886 at 6c0785b6c: Scene viewer extension to TrackViewer
- Pull request #892 at 1f5ba4c81: Signal Function OPP_SIG_ID_TRAINPATH
- Pull request #893 at bf8876b51: Signal errors
- Pull request #896 at 5866028cf: First implementation of https://blueprints.launchpad.net/or/+spec/specific-sounds-for-ai-trains
- Pull request #897 at 0a9d93913: feat: Improved system information collection
- Pull request #899 at e5db0a2dc: Duplex steam engines - Booster Engine addition
- Pull request #903 at c5f6638de: Downloading route content from Github
- Pull request #906 at 0e0aa8b41: Bug fix for https://bugs.launchpad.net/or/+bug/2047299 Crash loading a 3Dcab-only loco
- Pull request #907 at 9b0b04faf: Bug fix for https://bugs.launchpad.net/or/+bug/2047300 Dynamic tracks disappear after long tunnel