Add whitelist

A whitelist will override the normal proxy matching both in proxy.pac and in server processing. It will add flexibility to the tool to deal with complicated situations.

This is needed for the Sohu video app on iPad to work:
e.g.: 'http://220.181.19.218/*' is listed in unblock_youku.common_urls. However, a video file also takes a url like: 'http://220.181.19.218/ipad?file=*'. A white list will allow this video file to be downloaded directly.

Thanks.