Integrate functional tests in HDK installations

It would be a nice improvement to install the functional test system directly with the HDK.

This would in particular allow to generate automatically a testing command, similar to my personal scripts, that would pass all the interesting options (port, repositories root etc), making the development experience much more consistent.

IIRC the GDK already depends on Selenium and its Chromium driver. The only added dependency would be tox, and that's an easy one (I don't like to install it in virtualenvs personally, but the distro versions are fine in my experience).