Rendering/OpenXR: Add support for rendering controller models

Provide a way to render controller models (instead of the current green pyramids) until OpenXR provides some API to render controller models.

The approach of using the current interaction profile to pick an asset to render came from the OpenXR-Guide, here.

Models downloaded from sketchfab were free under a CC license, which is included for each model. So far, I have only found models for htc vive and valve index controllers. The models are not actually included in the repo due to their size and complications with making them available in build/install/packaged trees for both VTK and ParaView, without any duplication. Instead the models are available here, and will be packaged with paraview binaries by the superbuild. Also, the model archive can be manually downloaded and extracted into any build/install tree, and it will be found automatically by VTK.

It should also be easy to swap out the models for a completely different set without any code changes, see Rendering/OpenXR/README.md for details.

Below is a screenshot of the new HTC Vive models in action: