Add option to disable auto quit of driver in tests
New test: "throwWhenInteractingWithInvisibleElem"

Proves that Issue #156 is invalid.
Create the first Window of a Session on creation.

I was trying to be "smart" and delay the creation
of the actual Page/Window to the moment in which
the first interaction with it would actually
happen.

Unfortunately this clashes in a race condition
with the timer that takes care of deleting sessions
that have no more windows/pages: a newly created
session would be "windowless" until the first
interaction, and that would cause the issue.

Fixes issue #172.