Added experimental webgl work.

Webgl has a great deal of promise but the current state of the
Three.dart project in terms of stability and documentation makes it
difficult to use. May revisit the possible use of WebGl later.
Adding depth to the fish.

This produces a pleasing 3D effect without the need for complex 3D
packages. Currently the effect is like a collection of dust particles
suspended in water with gentle random turbulence.
Added demo3 featuring 3D (cheating) fish
Added post for 3rd demo