Joints: joint.reach (inverse kinematics), and a jointed part follows a drag (#1540)

Thanks @SychPL.

assets/locales/de.json

@@ -204,6 +204,7 @@
   "cmd.joint_motion_link": "Bewegungsverknüpfung",
   "cmd.joint_origin": "Gelenkursprung",
   "cmd.joint_rack_pinion": "Zahnstange und Ritzel",
+  "cmd.joint_reach": "Punkt anfahren",
   "cmd.joint_rigid_group": "Starrgruppe",
   "cmd.joint_screw": "Schraube",
   "cmd.joint_solve": "Gelenke lösen",