Visualization helper functions are inconsistent

[ma-sadeghi]

• Some of them return both the figure and axis handles, i.e., fig, ax, and some return just return the figure handle. I think they should all return both.
• Currently, they don't accept axis handle as an argument and instead they always create a new axis. In my experience, it's more common that plotting functions accept the axis handle for more granular control (like if you want to overlay them on an already existing axis, etc. Of course, it's still possible if you do the other plot afterwards)

[jgostick]

This is related to #849