Replace corner plotting with skopt plotting plot_objective

This issue was first mentioned in issue #1289, but that has since been split into two separate issues. This is dedicated to the plotting aspect but read the referenced issue for the original detail and context. The error handling will be handled separately and is not relevant to this issue.

Essentially in control.py there is a `plot_results()` function which calls a `create_cornerplot()` function. This should ideally be changed to utilise the `plot_objective` function in the sci-kit optimise library (skopt). Merely replacing the `plotter.create_cornerplot()` is not enough. It is necessary to pass in the results from a minimiser. Using a minimiser from skopt like `gp_minimize` could work but this needs a callable function to be passed to it. The surrogate function (from the sampled points of the original data) could theoretically be passed in as this callable function. This should be looked into.

The reason for this is that plot_objective allows from some nice plots which could definitely be useful to us.