Implementation of #129: Allow more tuning of the model hyperparameters.

[sandervh14]

====> Do not merge yet! See below for explanation. <=====

Story Title

#129 Allow more tuning of the model hyperparameters.

Changes made

Altered the constructor of both LogisticRegressionModel and LinearRegressionModel to support override of the default hyperparameters, via kwargs passing. Documented in the docstring of both models. See the issue description for more extensive explanation of why one would want this.

** Do not merge this yet with the Development branch. ** Unit tests have not yet been adapted yet. Was a speedy commit of an idea I was playing with in a notebook, when investigating how to further tune the models for a client. I'll take the time next week to adapt the unit tests.

How does the solution address the problem

This PR allows a data scientist to pass argument overrides for the constructor of the scikit-learn model used behind the scenes in Cobra, to try to tune further on a model's performance, if possible vs. Cobra's default settings for the model.

Linked issues

Resolves #129