Clean up front-end dependencies

[thibaudcolas]

Description

• Upgrade from Node 8 (EOL) to Node 14 (future LTS)
• Updates all development dependencies to recent releases without known security vulnerabilities
• Switches from node-sass to sass like our other projects
• Removes babel-polyfill – I don’t think we really need it for a project of this size, we only use ES6 syntax, not methods as far as I know. This amounted to nearly 80% of the project’s JavaScript.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[William-Blackie]

I've tested and am happy with the changes. @thibaudcolas. Will merge when I get access.