feat: add strict mode, add config file

[tomasvn]

added strict mode to prevent errors, cleaner code

[tomasvn]

@Pexeus I have added "use strict" rule, at the beginning of each file in setup, so now if you try to define for example this

function test() {
  test = document.getElementById(...)
}

it will throw Reference error so you have to set it to variable, either const or let so you would have

function test() {
  const test = document.getElementById(...)
}