Update dependencies

[linkmauve]

Supersedes #69, while also updating glutin to 0.31 and winit to 0.30.

These currently require raw-window-handle to be at version 0.5 to interoperate, until glutin gets updated to use 0.6.

I had to remove support for headless rendering, but will try to add that back at some point, if possible using EGL_KHR_surfaceless_context to avoid the dependency on winit in that case.

The event loop now runs forever and gets started in main(), instead of the previous way where it ran on demand from the GltfViewer. This accommodates for platforms which don’t let us run it on demand.

The second commit implements touchpad gestures, and has been tested on Wayland against https://github.com/rust-windowing/winit/pull/3656