Socks proxy support

Adds two configuration parameters, proxyServer and proxyPort, which in turn
enable socks5 proxy support in the driver.
While that would be ideal, unfortunately Tableau's UI asks for a "server", and so for the sake of consistency, since they would end up meaning the same thing, at the very least, the connection parameter name exposed to the user should remain "PROXYSERVER". I can change the names of the variables within the driver if you like, however.