Remove Sogou proxy code

From now on, we no longer support the embedded Sogou proxy in our `develop` branch. It's broken, irrelevant to maintain and will be removed in the next release.

Please use `-x` + ___your own proxy___ instead.

For Youku, we have an experimental `-y` option, in which you can make use of [Unblock-Youku](https://github.com/zhuzhuor/Unblock-Youku) using `-y proxy.uku.im:8888`. By far this option only works for Youku - soon it will be available for other sites like Tudou or Sohu.
**[Notice] [Unblock-Youku](https://github.com/zhuzhuor/Unblock-Youku) is another project. Read their [disclaimer](https://github.com/zhuzhuor/Unblock-Youku/blob/master/README.md) before you use their proxy.**

Closing #263 and #346 .