web: Rename 'First-person' -> 'Flight-cam'
web/boids.js: Add a per-boid size property

In future development, this could be used to rate the importance of a
boid, i.e. smaller boids could flock to larger boids.
web/boids.js: Remove CONSTANTS object

This was out-of-sync with the config options.
web/boids.js: Make min and max speeds depend on size

The speed of a boid is inversely proportional to it's size. This means
that smaller boids dart around quickly while larger boids lumber around
more sedately.
web/boids.js: Wing flapping rate is proportional to size
web/boids.js: Make cohesion and alignment dependent on size
web/boids.js: Introduce 'alpha male' mentality

A boid only registers another boid if it is larger than itself.
web/boids.js: Tweak configuration defaults