Implement unit testing and docstring updates.

[JacobBumgarner]

When developing VesselVio, I documented all of the classes and functions with comments. Ideally, I would've used docstrings, but at the time, I wasn't in the know!

Now, to improve the code, I want to convert the comments into docstrings to all of the classes and functions. In addition to this, I want to cover these functions with unit tests to ensure the longevity of the code. This documentation and unit testing will be useful for future Sphinx documentation builds, as suggested in #34.

Docstring Updates and Unit Test Implementations Checklist:
The progress of this task can be tracked in the maint/unit_docstring_update branch!
GUI:

• analysis_options_widget.py
• analysis_page.py (in progress)
  • Organization and Docstring Update
  • Unit Testing
• annotation_page.py
• graph_options_widget.py
• left_menu.py
• movie_widgets.py
• qt_objects.py
• stylesheets.py
• update_alert.py
• visualization_page.py

Backend:

• annotation_processing.py
• feature_extraction.py
• graph_io.py
• graph_processing.py
• helpers.py
• image_processing.py
• input_classes.py
• lee94.py
• movie_processing.py
• pk12.py
• qt_threading.py
• radii_corrections.py
• results_export.py
• volume_processing.py
• volume_visualization.py

[JacobBumgarner]

Just finished up with the annotation_processing.py cleanup update. Fixed a few bugs as well.

This will be addressed in PR #39.

Overview

annotation_processing.py has been converted into:

library/annotation/
- tree_processing.py
- segmentation_prep.py
- segmentation.py
- labeling.py