Annular simulation can now redo a time step.
Move `getDepostionRates` function from notebook to tools.py.
Notebook to evaluate changing controls for quirky simulations.
The advection equation was completely missing!

In the latest set of simulations the interfaces were completely
stationary because the advection equation has mistakenly been
deleted. The old value for the distance variable has also been removed
for no good reason other than that I don't completely trust how the
advection equation deals with old values.
Notebook includes images for broken simulations.