Vulnerabilities everywhere

Closes #678 (closed)

λ npm audit                                                            
found 11 vulnerabilities (10 moderate, 1 high) in 1812 scanned packages
  run `npm audit fix` to fix 1 of them.                                
λ npm audit fix                                                        
fixed 1 of 11 vulnerabilities in 1812 scanned packages                 
λ npm audit                                                            
found 11 vulnerabilities (10 moderate, 1 high) in 1812 scanned packages
  run `npm audit fix` to fix 1 of them.                                

• Some of the updates added postcss as a peer dependency, which means I had to add it as a direct dev dependency on the frontend.
• I moved mochapack to a dev dependency because it depends on mocha and webpack, which are both dev dependencies, and having it as a regular dependency caused warnings.
• I had to exclude package-lock.json from codespell because it tried to fix a "typo" in a checksum…
• 11 vulnerabilities remain:
  • css-loader should be bumped from 2.0.0 to 5.2.6, but this causes all CSS to break (#661 (closed)).
  • Webpack needs to be bumped to 5.38.1 due to one vulnerability in a dependency of Chokidar 2, which will not be fixed due to Webpack 5 now using Chokidar 3.
  • Waiting on https://github.com/sysgears/mochapack/issues/107 to fix two vulnerabilities from Mochapack (#676 (closed)).
  • Waiting on https://github.com/webpack/webpack-dev-server/issues/3407 to fix one vulnerability from webpack-dev-server.
  • I am still very unsure about what bumps should be done by other packages for the one remaining vulnerability (#677 (closed)).