RWGltf_CafWriter::ToEmbedTexturesInGlb() - added option embedding textures
into GLB file enabled by default.
Fixed uninitialized class field RWGltf_CafWriter::myIsForcedUVExport.
Image_Texture::MimeType() - added method returning MIME type based on image file format.
Image_Texture::WriteImage() - added method writing image into stream.