Replaced cli_webserver_workaround client option by a check of CONTENT_TYPE AND HTTP_CONTENT_TYPE entry in SERVER superglobal
[SoapClient] Fixed tests if proxy exists in environment variables
[SoapClient] Fixed typo for proxy options

Fixed #46
[SoapClient] Renamed proxy_user to proxy_login option to keep compatibility with SoapClient of PHP
[SoapClient] Added proxy authentication option in SoapClientBuilder

Fixed #47