style: Improve checklist menu design

[4ntsy]

Making checklist menus more consistent with the app design...

Since I don't know if it's of interest, it's more of an idea, but there are still significant improvements that can be made, not just to the design...

For example, the method that handles checkbuttons, the footer, and even these helpers, since the app code as a whole is very fragmented... It really needs refactoring... ^{but I don't have time for that because I would rewrite a lot of things...}

[psygreg]

I wrote the app as it currently is just to make it easier to keep track of what is what, since it was - and still is - my first time woking with Python. As long as improvements are made keeping the helper structure, I'm onboard.