Auto detect webdriver server

[Stuk]

Like Chromedriver is automatically detected on startup, it would be great if the webdriver server could be detected on port 4444 and a Firefox and Opera instance added if it is found.

[irinamok]

See issue #125. We decided to not to fix it, however, once we'll have support for IE, we might want to add all of them (Opera, FF, IE) if selenium server is detected