Create proxy around Mink's Session

[aik099]

Right now call to BrowserTestCase::getSession() will not only create session, but also start it automatically. The auto-start behavior comes from IsolatedSessionStategy.

This behavior might not be desired one, because browser is opened even before any user code, that interacts with it is started.

I think that we can create proxy around Session class, that would ignore explicit calls to start method and will auto-start (if not running) on call to ->visit method.