[WIP] Initial attempt at selenium stub for testing browsers

[ppietikainen]

Selenium webdriver allows for the scripting of browsers, which makes it possible to
test them with TryTLS. Unfortunately the level of control is pretty low (e.g. no HTTP status code
available, e.g. page title can be used to figure out whether load succeeded) + get_logs() returns
new log entries since last call to get_logs(), but end result could be useful.

[ppietikainen]

Now in testable state, Firefox seems to work, I couldn't figure out how to make chrome do cert checks, it now does something that should enable them, but doesn't. failing_titles needs review for both browsers, it now has the titles for both browsers.