Signatures: defining Mutation and Age

[ltbringer]

extends from #26

Needs a clearer definition of mutation and the way to generate signatures.

1. Each time a signature is created, it is assigned a value for mutation and health, all the values and the signature is persisted.
2. If a little mutation of the signature leads to different outcomes the mutation value is increased further and the signature still gets to participate in further tests and the value of health falls or stays same depending on the difference in the outcome.
3. If a signature does not lead to varying results its health is reduced and after N attempts it would become extinct, no more to be used in the test.