Allows AutobahnJS to be quieter

In several places, console.log was being called outside of a debug flag
guard. These changes define a ab._debugconnect flag, that can be set to
quiet console message during connect and hangup, if desired. The flag is
set to true by default, so there is no change in default behavior. If a
user would like to quiet said output, they need only execute something
like:

    window.ab._debugconnect = false;