web/boids.js: Preserve camera aspect ration on resize
web/boids.js: Add a baseline offset to separation slider

This enforces a minimum separation value for the boids which means that
reduces the chance of the boid geometries overlap and colliding when
separation is set to 0.
web/boids.js: Reduce the maximum separation value
web/boids.js: Use step size 1 for line-of-sight slider