2D yz quickplot not quite right

[rtimms]

For 2D (y,z) vars the plot should use pcolormesh rather than conotourf to give the correct result (for the way we have set up FEM the x,y values are at the corners of the mesh)

                if self.is_y_z[key] is True:
                    self.plots[key][0][0] = ax.pcolormesh(
                        x,
                        y,
                        var,
                        vmin=vmin,
                        vmax=vmax,
                        cmap="coolwarm",
                        shading="gouraud",
                    )
                else:
                    self.plots[key][0][0] = ax.contourf(
                        x, y, var, levels=100, vmin=vmin, vmax=vmax, cmap="coolwarm"
                    )