Bot improvements

[tim-we]

• all bots should try to avoid leaving the map / crashing into the boundary snake
• ScaredBots should also be scared of SnakeChunks, this would also solve collision avoidance with the boundary snake
• KamikazeBots
  • should only attack when the attack direction is correct. We could use the dot product of both snakes normalized direction vectors for that.
  • should spawn somewhat close to real players (perhaps only when real players are present)
  • should stop following a target after a while
• add new bot behaviors, e.g. there could be a HungryBot that always moved towards the closest food item or a MirrorBot that mirrors movements from another (nearby) snake

Related issue: #102

[tim-we]

Hungry bots have been implemented in #449