Minor bugfixes for gltf loading

Some minor bugfixes in this redo of 26 release:
 1) some gltf nodes crashed, those crashes are fixed
 2) there's now proper transparency support, especially for ml_gltf_all...
 3) our https://meshpage.org web page has examples of how to use it
     (browser dev console now prints the script that the web page is running, so that
      existing test cases can be used as a base for new content)
 4) as always, we'll be happy to hear any problems you've had with our software,
     so email us at terop@kotiposti.net if you find bugs or improvement suggestions