Adding proxy.harToFile().

Helps to dump the HAR content to a file.

Also, fixed issue with the way the Selenium Proxy
was created: the correct format is without a
"http://" in front of it, but just "host:port".
Adding tests that actually hook Proxy and Driver.

To do this on both local system and TravisCI I'm
using PhantomJS Driver.
Locally, it's easy to install.
On Travis is already available.