Building:
- The new tarball has reasonable build system so
build libgltf as external package instead of compiling
source files directly.
- Freetype dependancy is removed

Improvements comes with the new libgltf
- Can rotate the models too (orbit mode)
- Two camera handling mode: walkthrough and orbit
(press M to change).
- gltf_animation_set_time() works
- FPS can be displayed without freetype (press F)

Additional notes:
- There were some bugs/regressions which are fixed
during the integration (see patches).
- License files are uddated now.
- libgltf building is enabled only on those platforms
on which gltf support actually works (windows and linux)

Change-Id: Ia6c9c4da53a9b4fedba0d73aa5791489f8ad424b
Reviewed-on: https://gerrit.libreoffice.org/9895Reviewed-by: Zolnai Tamás <zolnaitamas2000@gmail.com>
Tested-by: Zolnai Tamás <zolnaitamas2000@gmail.com>