Reworked mutation:

- Difficulty won't start randomising until a player has left the safe zone.
- Times are adjusted now, easy and expert last 45-60 seconds. Normal and advanced last 15-45 seconds
- Rng of difficulty change is different now, each difficulty has probability weighting. Easy and Expert both have a 11.54% chance of being selected, whereas normal and advanced have a 38.46% chance.