Update for libmproxy 0.11

I've tried to use OpenWPM after an update of mitmproxy but it did not work. The first commite addresses some of the compatibility issue. 

Also I replaced "webdriver.close()" by "webdriver.quit()" which close the driver and frees memory instead of closing the window.

The second commit adds a new command "browse" to simulate browsing of a website (scrolling some pages and click on internal links)