fix the bug by taking the style directly from sns

[patrickleonardy]

Matplotlib styles bug fix

❗ Is the last change acceptable or will this break stuff? ❗

Changes made

• with plt.style.context("seaborn-whitegrid"): --> with sns.axes_style("whitegrid")
• with plt.style.context("seaborn-ticks"): --> with sns.axes_style("ticks")
• added tests to see if the plotting function throw errors or not
• changed the plotting such that they return a plot instead of showing it

How does the solution address the problem

By setting the styles directly with sns.set_theme we access the styles directly and do not rely on matplotlib to be up-to-date / have the same naming as we have in our code.

Additional thoughts

By setting the styles directly with sns.axes_style

Linked issues

resolves #184