Speed up the auto-re-normalize

[gully]

We saw a neat demo of the auto-re-normalize button for the dashboard. It's prohibitively slow, I think because we are making copies and making new fitting objects each time. I bet we could speed it up by surgically applying linear algebra to just the flux vector, while avoiding as many copies as possible. A key idea of the dashboard is to keep the latency to near imperceptible levels, for a really fascinating user experience.