Minor improvements and cleaning

[therealsujitk]

• Remove unused resources and redundant code (Cleanup and improvements #208)
• Update / Remove deprecated code (Cleanup and improvements #208)
• Move functions and rules into separate files (Cleanup and improvements #208)
  • Move JS functions into separate files (Ex: course-panel.js, timetable.js, course-list.js)
  • Move SCSS rules into separate files (Ex: course-panel.scss, timetable.scss, course-list.scss)
• Normalise variable names, ids and classes (Keep a consistent naming scheme) (Cleanup and improvements #208)
• Add Select All and Deselect All buttons to the slot filter
• Improve screenshots (Improved screenshots #189)
• Add the last updated semester in package.json (Added a last-update field #191)
• Update dependencies and devDependencies (Update node version and dependencies #237)
• Test an update node version (Update node version and dependencies #237)
• Add badges to README.md (Updated README.md #192)
• Update the README.md preview GIF
• Update CONTRIBUTING.md (Update contributing guidelines #195)
• Update issue templates with labels (Update issue templates #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. ~ #231 (comment)