Clean JS code

JS files (pages, components, classes ...) in the src folder are polluted by wrong practices. They need to be cleaned up.

To ensure a global formating on project files, we need to add a formatter tool. Prettier is great for this, and can be set as pre-commit hooks. It forces formatting with the same standard whenever a commit is added to the project. This allows to correct mistakes, thus creating a cleaner repository. Don't forget to verify conflicts with eslint and document this in the Contribution guide or README.md file.

To-do's:

• Add Prettier, Eslint, Husky packages as devDependencies
• Add scripts in package.json to lint and format code in src folder
• Add a configuration object in package.json for Eslint (with Airbnb base)
• Add a configuration object in package.json for Husky
• Add a configuration object in package.json for Prettier
• Document what this does in README.md
• Format src folder
  • Remove blank lines
  • Remove useless imports
  • Remove useless variables
• Clean src folder
  • Remove useless console.log
  • Convert wrong variables (var to const or let)
  • Correct wrong imports (require instead of import from)
  • Create global functions in Utils.js for re-used things (ex: url building from env variables like loginUrl)