Cookies refactoring

This change bring a behavior closer to RFC6265:
* non RFC6265 attributes are ignored, meaning that old attributes (version, discard, ports, comment and commentUrl) are been dropped
* as per RFC6265, a Set-Cookie header is not supposed to contain more that one cookie. Additional cookies are ignored (actually, everything after a comma)

Regarding performance, I haven't been able to tune Date parsing yet, and `Expire` attribute is the bottleneck. If there's no such an `Expire` attribute, this implementation is roughly 2,5x faster than old Netty based implementation.