1) Remove unnecessary includes of "Standard_OStream.hxx" file and add it only into files where it is really used.
2) Create the base interface for a file stream provider OSD_FileSystem and its inheritor OSD_CachedFileSystem that keeping last stream to be reused for opening a stream with the same URL.
3) Use OSD_CachedFileSystem object instead of RWGltf_GltfSharedIStream during Gltf reading.
