Mutate "repetitions per branch" incrementally #121

Currently the "Repetitions per branch" option is able to mutate to a large number right away, however I think it would be better if the mutation simply added or subtracted from the value. This is because a large number tends to create an organism that isn't able to survive because it's essentially several organisms stuck together, but if the repetitions were more gradual it would maybe allow the organism to gradually mutate this value higher over time and do other mutations in the meantime to allow it to survive.