Add support for cookies set by a proxy

Hi, love your proxy, works great and I had it setup within minutes.

Recently ran into an issue though where our local server and the remote proxy server were both using the same Cookie name (JSESSIONID).  The proxy request to the remote server would then send the local cookie and the remote server would respond with 403 access denied because it doesn't know anything about that session.

I thought about modifying your code to be able ignore sending the Cookie http header (which would have worked for our situation) but instead decided to allow the remote proxy to set cookies by rewriting the cookie paths and names.

Let me know what you think.
Thanks