Refactored labeled.py file

[GoThrones]

Overview: What does this pull request change?

This PR refactors LabaledLine and LabeledArrow class in labeled.py file. Also adds docstring to it.

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

Label positioning was not good enough. Now, via this PR, users will have option of where to place the label, w.r.t the Line/Arrow. Also, the scaling wasn't working properly before. But this PR allows scaling to happen not to the label, but only to the Line/Arrow.

test_LabeledArrow was failing, because this PR modifies the scale method applicable to LabeledLine and LabeledArrow class. Therefore, a new npz file: LabeledArrow.npz has been created.

Further Information and Comments

Output of the example code in docstring, for Line and Arrow:

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