Refactored the code and improved the docstring of vector_field.py

[GoThrones]

Overview: What does this pull request change?

This PR makes a minor alteration in the code of ArrowVectorField class and StreamLines class. Improves the docstring of all three classes in vector_field.py

Motivation and Explanation: Why and how do your changes improve the library?

The code related to x, y and z ranges was duplicated in ArrowVectorField class and StreamLines class. I've put that code in VectorField class, and the ArrowVectorField and StreamLines class invoke the method _setup_ranges() to setup the ranges.

The docstring were misleading at few places. The parameters were not explained properly.

Links to added or changed documentation pages

Further Information and Comments

Reviewer Checklist

• The PR title is descriptive enough for the changelog, and the PR is labeled correctly
• If applicable: newly added non-private functions and classes have a docstring including a short summary and a PARAMETERS section
• If applicable: newly added functions and classes are tested