Render goals and targets

In both the rl and the electrofish trajectories, the robot always has a target point and commonly also a goal.

The target is the point where the robot itself is moving, determined by the current action. The goal is determined by the task and is often the point where the robot should lead the fish.

The goal is rendered as X. The target is not rendered as one point, but instead as a dotted line from robot to target, which somehow was easier to understand when things move quickly.

In the screenshot the robot moves to the goal, so the target and the goal are at the same point.