Fix semantics of Fitness comparison
Created by: gkirgizov
This PR changes meaning of Fitness comparison. less means worse, so if f1 > f2 then f1 is better than f2.
In other words, Optimiser now performs maximisation on Fitness objects.
But internally, Fitness objects compare their metric values as if we minimised metric values.
Rationale: HallOfFame from Deap internally compares fitnesses in this way. Fedot uses HallOfFame, so Fitness must follow its contract.
Example: this statement is true SingleObjFitness(-0.85) > SingleObjFitness(-0.75)