feat(ui): add changelog window

[CyanVoxel]

Summary

This PR adds a new "Changelog" window that displays a styled version of the changelog in-app. This changelog window is automatically opened after the program is detected to be ran with a version newer than the previous version known (if any), and will not be shown upon a fresh installation. This window can also be accessed from Help -> View Changelog.

The changelog content is taken from the local CHANGELOG.MD file (that's also now bundled in pyinstaller builds of the app), and images are pulled from their online sources. This means that the changelog will display while offline, but images won't load. I've also designed the changelog to not render all at once, and slowly add additional sections and request any new images as the user scrolls further down.

Images have a maximum height and width for this window, but will otherwise (try to) respect their original dimensions.

NOTE: A lot of the styling for this is now shared with the "About" screen, which doesn't yet use the "Modal/ModalContent" system. I'll convert that window into the modal system with an MVC split and see what code I can reasonably share between these two windows in a separate PR.

Tasks Completed

• Platforms Tested:
  • Windows x86
  • Windows ARM
  • macOS x86
  • macOS ARM
  • Linux x86
  • Linux ARM
  • Nix Flake
  • Python module with -m
• Tested For:
  • Basic functionality
  • PyInstaller executable