Replace custom UI elements with a library.

[ben-ryder]

Describe your improvement
It is probably a good idea to look at replacing as many of the custom GUI components as possible with components from a UI library.
A quick look around and pygame_gui (https://github.com/MyreMylar/pygame_gui) looks like a good choice.

Is your suggestion related to any problems?
Not specifically, but this might make the GUI easier to maintain & work on.

Additional context
n/a