Add config for running Pucauto behind a proxy

[tomreece]

A user named Geoff needed to run Pucauto behind a proxy, figured out how to do it on his own, and sent me the following code snippet of his solution. Make this a configurable option.

from selenium.webdriver.common.proxy import *
...
PROXY = "<server>:<port>"

myProxy = Proxy({
    "httpProxy":PROXY,
    "ftpProxy":PROXY,
    "sslProxy":PROXY,
    "proxyType":ProxyType.MANUAL,
    "class":"org.selenium.Proxy",
    "autodetect":False
})

DRIVER = webdriver.Firefox(proxy=myProxy)