Initial mesh support

[thangngoc89]

Hi,

Thanks for making niivue-react! I’ve been using it for a while now, and it’s been awesome. Your diffing method is genius—way better than the way I was reacting (pun intented) to props changes in my old implementation. I ripped it out as soon as I see yours.

Recently, I needed mesh support for my project, so I put together this PR.

Right now, the support is pretty basic but gets the job done:

• Load/remove mesh
• Change mesh property (rgba255, visible, ...)
• Change niivue's instance meshXRay

I’ll add more features as I need them for my project.

Cheers

[jennydaman]

Amazing! I’ll review later today or tomorrow.