Making Lotka–Volterra example more interesting.

Currently the solution to the Lotka–Volterra Chebgui demo
looks just like a sine and cosine. I have changed a couple
of constants to make the solution look more interesting
and asymmetrical.
Making the VDP test be a proper test.
Changes so that we still respect TRIGTECH discretization.
Merge branch 'fix-guiDemo-lotka' of github.com:chebfun/chebfun into feature-firstOrder-reform