This commit adds several components to centralize and extend 3D media loading. They are not yet integrated into Viewer3D. The entry point to this system is the MediaLibrary component that:
* can load N medias based on a filepath or load-and-watch node attributes
* provides a cache mechanism to instant-reload medias that were unloaded under certain conditions
* gives access to statistics (vertex/face/camera/textureCount) through a unified interface
