Proxy settings

If there is no proxy injected in the constructor, then the proxy is always null, but you could a default have proxy settings defined in app.config like this:

 <system.net>
    <defaultProxy enabled="true">
      <proxy proxyaddress="http://127.0.0.1:8888"/>
    </defaultProxy>
  </system.net>

This commit fixes this issue, and allows the use of a default proxy if there is none injected in constructor.