Add a tunnel for directly managing webdriver binaries

[jason0x43]

See https://github.com/theintern/intern/issues/314

Intern currently uses Selenium to manage browsers, which requires Java. The Java requirement is becoming more of a burden as time goes on, and most browsers have native WebDriver drivers at this point, so it would be worthwhile to add a tunnel class that could work with them directly. We already have logic in SeleniumTunnel to retrieve tunnel binaries; we'll just need to be able to configure and launch them.

[vladikoff]

👍 this would be great! I heard it will also be a speed boost (by eliminating the "java" layer)