Goal Bias should be implemented by modifying random pool instead of going directly towards goal

[jgkamat]

Right now goal bias is just a percentage chance that we go directly towards the goal, it should be modified to be changing the probability function itself, so that we don't just go towards the goal when we do choose to do so (but we have a higher probability of going some direction closer to the goal). This will help us go around obstacles better while still having a high goal bias.

Suggested by @barulicm