Minor changes required

[trolit]

@Dorota1997 consider following things to add / change in the portfolio and make feature/ for it?

• some tags should have self-closing (e.g. About.js).
• apply single convention to spacing (e.g. About.js)
• add Prettier and ESLint with desired config so future PR's are more convenient to review
• review all files and use const / let instead of var
• some inline styles could be moved to scss files like that one.
• add Idelavois portfolio adaptation in README.