cgmath version 0.18 and automatic arcball camera placement

[beltegeuse]

Hi Will,

Please find a pull request that implements two changes:

1. Bump cgmath to last version (0.18).
2. Compute AABB from the loaded obj to automatically place the camera for obj_viewer and obj_ao_parallel. This changes the support display struct and adds a new aabb struct.

Best

[Twinklebear]

Thanks @beltegeuse , this looks good! Having automatic placement of the camera will be great for the demo apps. I think the only change needed is how the arcball crate is being included.

I've also been (slowly) working on refactoring the codebase a bit to fix the lifetime annoyances, and to also move the viewer to a wgpu-rs based one, since glium is in maintenance mode and I was having some issues with it and related libraries.

[Twinklebear]

Thanks @beltegeuse , this looks great!