Visualization/plotting module

[rickvanveen]

Is your feature request related to a problem? Please describe.
Frustrating to come up with the same kind of visualizations, i.e., discriminant plots, relevance diagonal/off-diagonal, learning curves, and possibly others.

Describe the solution you'd like
Add visualization module (matplotlib) for common visualizations.

Describe alternatives you've considered
Could be implemented using other plotting library. However, matplotlib works for the documentation and in publications.

Additional context
N/a