Make org.openqa.selenium.Cookie serializable

Sometimes we need to store cookies in MongoDB so we need either Cookie to be serializable or to write some wrappers to perform this. As Cookie was not serializable this made us to write wrappers and use them every time we want to store cookie in MongoDB but this seems to be useless extra work so in this pull request i made Cookie serializable and wrote simple test to check, that cookie correctly serializes and deserializes.