Fix memory leak in OpenGL visualizer (#3533)

Fixes #3530

Description of changes:
- free memory of quadric objects; they caused a 12 MiB/min memory leak in simulations containing bonds and a 3 MiB/min memory leak in simulations containing cylindrical shapes (`Cylinder`, `SpheroCylinder`, `SimplePore`, `Slitpore`)
* fix an issue in the `visualization_constraints.py` sample that prevented a `Slitpore` from being added to the list of constraints

samples/visualization_constraints.py

@@ -30,7 +30,7 @@
 group.add_argument("--wall", action="store_const", dest="shape", const="Wall",
                    default="Wall")
 for shape in ("Sphere", "Ellipsoid", "Cylinder", "SpheroCylinder",
-              "Stomatocyte", "SimplePore", "SlitPore", "HollowConicalFrustum"):
+              "Stomatocyte", "SimplePore", "Slitpore", "HollowConicalFrustum"):
     group.add_argument("--" + shape.lower(), action="store_const",
                        dest="shape", const=shape)
 args = parser.parse_args()
@@ -62,51 +62,53 @@
         dist=20, normal=[0.1, 0.0, 1]),
         particle_type=0, penetrable=True)
 
-if args.shape == "Sphere":
+elif args.shape == "Sphere":
     system.constraints.add(shape=espressomd.shapes.Sphere(
         center=[25, 25, 25], radius=15, direction=1),
         particle_type=0, penetrable=True)
 
-if args.shape == "Ellipsoid":
+elif args.shape == "Ellipsoid":
     system.constraints.add(shape=espressomd.shapes.Ellipsoid(
         center=[25, 25, 25], a=25, b=15, direction=1),
         particle_type=0, penetrable=True)
 
-if args.shape == "Cylinder":
+elif args.shape == "Cylinder":
     system.constraints.add(shape=espressomd.shapes.Cylinder(
         center=[25] * 3, axis=[1, 0, 0], direction=1, radius=10, length=30),
         particle_type=0,
         penetrable=True)
 
-if args.shape == "SpheroCylinder":
+elif args.shape == "SpheroCylinder":
     system.constraints.add(
         shape=espressomd.shapes.SpheroCylinder(center=[25] * 3, axis=[1, 0, 0],
                                                direction=1, radius=10, length=30),
         particle_type=0,
         penetrable=True)
 
-if args.shape == "Stomatocyte":
+elif args.shape == "Stomatocyte":
     system.constraints.add(shape=espressomd.shapes.Stomatocyte(
         inner_radius=3, outer_radius=7, axis=[1.0, 0.0, 0.0], center=[25] * 3,
         layer_width=3, direction=1), particle_type=0, penetrable=True)
 
-if args.shape == "SimplePore":
+elif args.shape == "SimplePore":
     system.constraints.add(shape=espressomd.shapes.SimplePore(
         center=[25, 25, 25], axis=[1, 0, 0], length=15, radius=12.5,
         smoothing_radius=2), particle_type=0, penetrable=True)
 
-if args.shape == "Slitpore":
+elif args.shape == "Slitpore":
     system.constraints.add(shape=espressomd.shapes.Slitpore(
         channel_width=15, lower_smoothing_radius=3, upper_smoothing_radius=3,
         pore_length=20, pore_mouth=30, pore_width=5), particle_type=0,
         penetrable=True)
 
-if args.shape == "HollowConicalFrustum":
+elif args.shape == "HollowConicalFrustum":
     system.constraints.add(shape=espressomd.shapes.HollowConicalFrustum(
         r1=12, r2=8, length=15.0, thickness=3,
         axis=[0.0, 0.0, 1.0], center=[25, 25, 25], direction=1),
         particle_type=0, penetrable=True)
 
+else:
+    raise ValueError("Unknown shape '{}'".format(args.shape))
 
 for i in range(100):
     rpos = np.random.random(3) * box_l