(Refactor) Eslint+prettier configuration

(Mandatory) Description a human-readable description of changes:
- eslint configuration is added
- prettier configuration is added
- babel configuration is added
- node version in .nvmrc is increased to the latest LTS version 8.11.3
- npm run lint command is added to fix style of coding with npm run lint -- --fix
- all sources are fixed with the command ☝️
a human-readable description of the purpose of the PR:

In order to make the code standardized eslint + prettier configuration were added. It will make code more human-readable.
(Mandatory) What is it: (Fix), (Feature), or (Refactor) in Title, e.g., "(Fix) price of 1 token in Wei > 18 decimals" (Refactor)
(Mandatory) Developers: Each completed PR should be updated in the Wiki Documentation. (Recommended) Each PR should have one commit message and therefore should only contain one specific fix or feature. Otherwise, multiple PRs should be made
Did you check that your PR is chain agnostic? It shouldn't depend on any hardcoded chainIds, URLs. Yes
(Optional) Any additional concerns or comments

poanetwork / poa-dapps-validators