[Date] Usage of the Date object

Dates.js

## randomDateInRange
randomDateInRange(start, end) {
  return new Date(
    start.getTime() + Math.random() * (end.getTime() - start.getTime())
  );
}
randomDateInRange(new Date(2018, 0, 1), new Date(2018, 3, 1)).toLocaleDateString();

randomDateAfterDate(start, days) { 
  return new Date(
    start.getTime() + (Math.random()*days*24*60*60*1000)
  ); 
}