Minor improvements and cleaning

[therealsujitk]

• [x] Remove unused resources and redundant code (#208)
• [x] Update / Remove deprecated code (#208)
• Move functions and rules into separate files (#208)
  • [x] Move JS functions into separate files (Ex: course-panel.js, timetable.js, course-list.js)
  • [x] Move SCSS rules into separate files (Ex: course-panel.scss, timetable.scss, course-list.scss)
• [x] Normalise variable names, ids and classes (Keep a consistent naming scheme) (#208)
• [ ] Add Select All and Deselect All buttons to the slot filter
• [x] Improve screenshots (#189)
• [x] Add the last updated semester in package.json (#191)
• [x] Update dependencies and devDependencies (#237)
• [x] Test an update node version (#237)
• [x] Add badges to README.md (#192)
• [ ] Update the README.md preview GIF
• [x] Update CONTRIBUTING.md (#195)
• [x] Update issue templates with labels (#211)

Note: Most editors like Visual Studio Code or IntelliJ show you what is deprecated with a strikethrough.

[vatz88]

Updating CONTRIBUTING.md can be a separate issue and PR

[therealsujitk]

@vatz88 when free, do you think you can add the hacktoberfest topic to this repository so that PRs will count as valid contributions during this event. As of October 2021 they said only if a repository has this topic or if PRs have a hacktoberfest label they will be counted as contributions.

[vatz88]

@therealsujitk done

[therealsujitk]

I've added updating the node version as a task here. ~ https://github.com/vatz88/FFCSonTheGo/issues/231#issuecomment-1785983401