feat: Loading animation + Preloading Images

[darren2hang]

• Implement a Preload Component that loads the images that are passed to its props
• it uses CarouselContext to move to the next slide once the preloading is done
• The Preload Component uses a Promise when loading the images
• require.context() is used to get all the images inside a folder

closes #197 closes #162

[reginawang3495]

• cleaned up assets folder and updated folders to preload Preload
  • this is so the preloading of files isn't as ugly and is more streamlined
• moved preloading to Carousel
• removed unnecessary code
  • GIFPlayer
  • unused props in Carousel
  • unused images
  • unnecessary eslint-disables
• updated linting a bit
• other final spruce ups
  • increased animation times for several slides in Activity3
  • updated messed up bolding in A2 and A3
  • other smol cleanups

[mergify[bot]]

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