[GeoMechanicsApplication] Extend the JSON file reader such that it can read points and lists of points

[avdg81]

At present, inputting lists of points is cumbersome, since the JSON file reader doesn't support reading lists of points. The current workaround is to specify three lists: one containing all the x coordinates of the points, one for the y coordinates, and one for the z coordinates. The more natural way would be to have a single list of points, i.e. [[x1, y1, z1], [x2, y2, z2], ... [xn, yn, zn]].