fixed visualization of attraction and repulsion
Just for the record: tried kicking out task interference from old
velocity, which removes the transitory influence of objectives on
tasks, but also makes converge super slow again. I think we can live
with transitory influence from objectives into tasks, because the
steady state respects the tasks, and convergence is much faster.
Tweak timestep to converge much faster. But in the end I think the
tasks should run directly in velocity space, or maybe even in position
space.