Simulate with obstacles which change shape over time?

[timmercy]

Do we want to add functionality to simulate what happens if obstacles change shape during the movement of the vehicle? E.g. while moving, more information becomes available and it turns out that a circular obstacle actually has a slightly larger/smaller radius.

Required adaptations:
- Change environment.obstacles[].shape.radius to the new value
- Call _prepare_draw() of obstacle.shape (to update self.plt_lines, and the environment plot)

These functionalities can maybe be implemented by extending the trajectories attribute, which allows the user to define obstacles which start to move at a certain time? Then the user can e.g. state that at time t=2s, the radius will get a new value. This would require adding radius as an attribute of signals.

When using only the Deployer, this functionality already works.