Implement custom class for generations

[MorrisNein]

This PR is addressed to solve the following issues:

• #900
• #846

Also makes a step towards #866 (labeled generations are planned, possible with custom values).

Work in progress:

• [x] Move OptHistory and related objects to a separate repo.
• [x] Implement custom classes for individuals storage: IndividualsList & Generation.
• [x] Make the new classes responsible for consistency of individuals during the optimization by implementing individuals_pool context variable.
• [x] Wrap the optimization process into the new context. Test consistency of the resulting history with & without multiprocessing.
• [x] Add type hints for Generation methods.
• [x] Unify Generation class usage in Optimiser.
• [x] Set signatures of historical operators for working with IndividualsList or Generation instead of PopulationT (where it is necessary).
• [x] Add ability for generations labeling & other metadata.
• [ ] Add final choices to OptHistory.
• [ ] Adapt OptHistory serialization.
• [ ] Develop readable representation for IndividualsList & Generation.

An alternative solution: try using custom serialization class.