introducing cookie object

* created cookie as a mysfw's module
* moved `request::allows_cookies` to `cookie::are_accepted`

**To be discussed :**
`cookies::set` and `cookies::delete` both use `setcookie`, a function that return false if some data has already been sent on stdout.
Should they return true or false or always return `$this` and throw an exception when `setcookie` returns false?