[LOW] Contour plots of particle dimension

[eibar-flores]

It would be nice to add contour plots of state variables (concentration, potential, etc) as a function of the electrode dimension (x) and the particle radial dimension (y). They can act as snapshots of the state of the cell, such that when the time slider is changed, the contour plots update. They are interesting to evaluate whether the state variables are accumulating at either of the radial or electrode dimensions of the model.