Cookie object implemented

The Cookie object is a very simple object that acts as a representation of a key value pair, but with the immutable object pattern to avoid other classes editing their value on-the-fly.

"The practice by which changes result in a new instance is termed immutability, and is a feature designed to ensure the integrity of a given value".

This is important with Cookies, because once they are set on the Request/Response, they object representation shouldn't be changed without being set again.