Adds several features and fixes

[Gudine]

I took the opportunity to add a few contributions to this project, such as:

• Add a new changelog system that stores changelogs in the dataset itself.
• Add a dark mode toggle, to resolve Dark Mode #11
  • Replace white background images with transparent versions, to work better with the new dark mode
• Allow for different image sizes/aspect ratios
• Neutralize Undo button at the start of the sorter, to fix Undo bug #16
• Some other code refactors that don't change behavior

There's also a live demonstration.

Some of those changes would break the existing website, as they change the file names. To help with that, I made a branch that has the same datasets as the website, but replaces the image paths accordingly. So you can just replace the website's files with those.

[Zanes]

Do you know how would one go about making a feature to skip a character completely?