Gltf animation support (#1551)

* Added example for gltf animation and split some functions for loading model animations into IQM and GLTF similar to how models are being loaded.

* Removed wrongly duplicated function

* Bone loading for gltf model (not working at this point)

* Loading info about vertex to joint connection but animation is still not working

* Skeleton and pose is correctly loaded. Need to communicate about interpolation in GLTF

* The model almost looks like a real person on animation.

* Fixed model loading with bones.

Also updated license info on the model.

* Cleaned up some code and updated examples.

* Fix identation issues

* Fix identation issues

* Fix identation issues

examples/models/resources/gltf/LICENSE

@@ -0,0 +1,11 @@
+Rigged Figure model has been created by Cesium (https://cesium.com/cesiumjs/),
+and licensed as Creative Commons Attribution 4.0 International License.
+
+Check for details: http://creativecommons.org/licenses/by/4.0/
+
+Avocado model is provided by Microsoft
+and licensed as CC0 Universal Public Domain
+
+Check for details: https://creativecommons.org/publicdomain/zero/1.0/
+
+GLTF sample models for testing are taken from: https://github.com/KhronosGroup/glTF-Sample-Models/