Update coloring function and adjust interface

[tyshoe]

This PR changes the way that the color substitution is applied. Before, your new values would be added to the original RGB values, now it will be fully replaced. Additionally, the code as been converted to a class based approach, which simplifies structure and allows for more easy additions for functionality.

Features

• added requirements.txt
• added images folder for images in README.md
• added items for adjustments and improvements in README.md
• adjusted README.md to reflect UI and requirements changes
• adjusted input method for filter (selected pixels to change colors)
• adjusted input method for edit (applying color to selected pixels)
• adjusted apply button (now applies alpha, rgba channel, and colors at same time)
• added ability to change file type when exporting
• added scaling image to size of window
• convert to class based approach
• convert to customtkinter

File structure and intent

• main.py is where the app is run, also includes many functions passed to menu
• menu.py is where the tab menu is held
• panels.py is where all of the panels for the menu is held
• canvas.py is where the canvas for the image is held
• images folder is for README.md images

User Interface

Before:

After:

This is a rather large pull request and should definitely be broken down in the future, but after some collaboration this shouldn't be too hard to move forward with.