use java.net.HttpCookie instead of Crockfords json.org

The org.json.Cookie class from Crockfords json.org library is licensed under
an MIT like license but with an added clause:

"The Software shall be used for Good, not Evil."

For this reasons the library is considered non-free software by Google,
Debian, Fedora and others. The android project wrote a white room
reimplementation[1] but it does not (yet) include the Cookie class.

[1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=697311

Issue: http://code.google.com/p/google-web-toolkit/issues/detail?id=7885
Change-Id: If3568a459f7a196140fa7af5b38850716a71fdd6
Review-Link: https://gwt-review.googlesource.com/#/c/1600/

Review by: skybrian@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@11457 8db76d5a-ed1c-0410-87a9-c151d255dfc7