ui-finc-config: add rules for eslint, add config file for prettier

1. First step: Add important rules for eslint

2. Check if we like to have a prettier configuration for the existing eslint rules (see 1. First step).
   Add a config file .prettierrc for using the same prettier configurations, for example:

• Add a file .prettierignore for files which should be excluded from formatting:
  _{# Ignore everything by default
  **
  # Re-include only .js files
  !*.js}

We could use Husky for using prettier via pre-commit:
https://github.com/typicode/husky

In package.json:
for execute via npm run format
"scripts": { "format": "prettier --write '**/*.js'" },
for execute automatically on git commit
"lint-staged": { "*.js": "prettier --write" }