Add GUI to main branch.

[ms1450]

GUI Implementation

Description

Added GUI functionality to the main branch. Created 'main_cli.py' which will be an alternative to 'main.py' as a CLI for the program.

Type of change

• [x] New feature (non-breaking change which adds functionality)
• [x] Breaking change (fix or feature that would cause existing functionality to not work as expected)

How Has This Been Tested?

• [x] customer_sheet_1.csv
• [x] customer_sheet_2.csv
• [x] customer_sheet_3.csv
• [x] customer_sheet_4.csv
• [x] customer_sheet_5.csv
• [x] customer_sheet_6.csv
• [x] customer_sheet_7.csv
• [x] customer_sheet_8.csv

Checklist

• [x] My code follows the PEP8style guidelines.
• [x] I have performed a self-review of my code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules