GLTF Punctual light support

[LeonBrands]

Is your feature request related to a problem? Please describe.
My use case uses Blender for level design, and all static geometry is loaded in as a single model (with sub-meshes) from a GLTF file. This limits me in some aspects as I can not simply edit in light sources into the "scene".

Describe the solution you'd like
Since we use Blender for level editing, it'd be very convenient if lights could also be configurable through Blender. This is possible by supporting the GLTF 2.0 KHR_lights_punctual extension enlisted here https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Khronos/KHR_lights_punctual

Describe alternatives you've considered
Other alternatives would include a custom editor or scene file, both of which would take significantly more time. Supporting the lights extension should take fairly little time and would greatly expand the flexibility of the model loader.

I'm willing to take this upon myself once I have the time but if anyone else is able to start on this sooner then that'd be greatly appreciated as well.