Panda3d-gltf

Converter
* Add texture and material attribs to fallback RenderState
* Add option to convert PBR glTF materials to "legacy" materials
* This is best effort and data *will* be lost
* Exposed in `GltfSettings` as `legacy_materials` (defaults to `False`)
* Exposed in `gltf2bam` as `--legacy-materials` flag

Converter
* Add support for joint/bone parents
* Add support for PANDA3D_physics_collision_shapes extension (includes new intangible setting)
* Fix errors when using double-precision builds of Panda3D
* Fix ZeroDivisionError when loading single-frame animations
* Fix loading meshes with no indices
* Fix loading model tangents on Z-up files
* Fix generating tangents on Z-up files
* Fix the sign on generated bi-tangents

Converter
* Fix error when no top-level `extensions` object is present
* Fix crash when using Panda3D compiled with double-precision floats
* Add support for emission maps
* Fix direction and lens view vector for directional lights
* Do not assign empty TransformBlendTable if a Geom does not have a `transform_blend` column

Viewer
* Improved default camera position and view
* Add work-around to make lights from the model work
* Upgrade to `panda3d-simplepbr>=0.6` for emission and occlusion map support
* Shortcuts added to toggle various render features:
* n: toggle normal maps
* e: toggle emission maps
* o: toggle occlusion maps
* a: toggle ambient light

Other
* Add `--version` flag to CLI
* Use `GltfLoader.global_settings` if `gltf_settings` is `None` for `patch_loader()`

Viewer
* Toggle wireframe view with `w`
* Toggle textures with `t`
* Dump scene graph to standard out with `shift-l`
* Dump analysis of the scene graph to standard out with `shift-a`

Converter
* Fix an issue where morph targets would no longer be bound after saving and loading to model cache

Converter
* Add `--no-srgb` option to skip making sRGB textures (not spec-complaint, but may be useful for some workflows)
* Add options to copy textures
* Add support for morph targets and animations
* Add support for multiple meshes using the same skin
* Add support for skeletons with multiple root bones
* Fix some transformation issues with characters
* Fix color of fallback normal map
* Fix texture stage order (make it deterministic)
* Fix fallback textures not getting saved to BAM files

Many thanks to el-dee and rdb who did most of the work for this release!

Converter
* Faster loading of bin files
* Support loading supplied tangents
* Calculate tangents if they are missing
* NOTE: this is still WIP and not spec-compliant
* Support loading normal maps
* More axis-conversion fixes

Viewer
* The default camera will now look at the loaded model