Add common usage explanations and code examples to qiskit.visualization module level API reference page.

[HuangJunye]

What should we add?

As part of the new Qiskit Documentation content restructuring, we are deprecating Qiskit Visualizations tutorial and moving the content to API reference: Qiskit/qiskit-tutorials#1436

@Guillermo-Mijares-Vilarino have improved the code examples and explanations for a few ploting functions. But we still need to add usage explanations and code examples that are common to most (if not all) plotting functions, such as title, figsize, color ax to the module level API page