Change k0 to be scaled by Lp

[Raymond Smith]

It makes more sense for the reaction flux to be scaled to an actual length scale such that non-dimensionally

Flux = k0/e*BVfunction

and then for homogeneous and/or ACR particles, a Area*Length/Volume = delta_L factor is required such that

dc/dt = delta_L*k0/e*BVfunction

I'll write it this way in the documentation, so might as well change it in the code.

[Raymond Smith]

Fixed in commit dd41fdd.