Refactor objective in optimizer

[maypink]

There is a need to evaluate graphs and pipelines in side mutations from optimizer (e.g. Sructural Analysis). On the one hand, current objective property does not allow to do such evaluations since there is no referenced data in it. And on the other hand, self.eval_dispatcher._objective_eval is fine for evaluating pipelines, however this function does not provide any information about calculated metric's names. That is precisely why objective should be modified. Current solutions is to construct new mixed objective like this: objective is this class is self.eval_dispatcher._objective_eval