add pre-reach "aiming" response

[thartbm]

For each kind of reaching task (cursor, no-cursor or error-clamp), add an option that before reaching, people see the target and can change the orientation of an arrow that starts at the home position and extends one third or one half of the home-target distance to indicate where they think they will move their hand/mouse. They use the arrows keys on the keyboard (with the hand not on the mouse) to do this, and press another button to key it in. The arrow can go from -30 to 210 degrees, and should appear at some position that is not always the same (what makes sense here?). The angle of the arrow that participants key in should be stored in a column in the data, and not interfere with the pre-processing of the other data. However, it should be possible to get aiming errors instead of cursor or hand deviations in the data processing step.