Phase Plane: make the number of integration time steps a configurable parameter

It would be nice to be able to set the number of integration time step in the phase plane.
Increasing the integration time step size is not the solution, since a large value could lead to numerical instabilities in certain models (eg, Epileptors, SJ3D), and working with this parameter would be misleading (although the technical effect is the same).

To avoid slowing down this page, a maximum number of steps should be imposed.