Example methods to add to the main library

[dmccloskey]

Description

Several experimental extension methods for PopulationTrainer and ModelReplicator have been implemented. It would be good to move them to the classes and provide unit test coverage

Objectives

• [ ] Add setPopulationSizeFixed to PopulationTrainer
• [ ] Add setPopulationSizeDoubling to PopulationTrainer
• [ ] Add setTrainingStepsByModelSize to PopulationTrainer
• [ ] Add setModificationRateByPrevError to ModelReplicator
• [ ] Add setModificationRateFixed to ModelReplicator
• [ ] Add unit tests for PopulationTrainer
• [ ] Add unit tests for ModelReplicator

Validation

• [ ] Passing unit tests