custom eslint rules to enforce conventions

[FrancescoCioria]

original issue: https://github.omnilab.our.buildo.io/buildo/labonline/issues/1305

requirements

eslint can be very effective to enforce some conventions. We're already using it to verify if a component's name is the same of its filename.
New rules to help us enforce some conventions::

• a Component can import only one sass file and only if it has the same name (but in camelCase)
  • ex: MyBeautifulComponent can have import './myBeautifulComponent.scss'
• the imported sass must be in the same folder (./*.scss)
• if a component has a main class, this should be the component's name in kebab-case
  • ex: MyBeautifulComponent can have <div className='my-beautiful-component' ...