Hyperparameter improvements

Improvements to the HyperParameters object. Now you have to set bounds. Hyperparameters created from a nested dictionary structure, allowing them to be stored as JSON. Below is an example.

from model_builder import HyperParameters

hyperparameters_dict = {
     "learning_rate": {"min": 0.0001, "max": 0.001, "start": 0.0001},
     "epochs": {"min": 1, "max": 100, "start": 2},
     "validation_split": {"min": 0.1, "max": 0.3, "start": 0.2},
}

hyperparameters = HyperParameters(**hyperparameters_dict)

Also ensured that learning rate is now used, which was previously forgotten.