Display a warning on queue related commands when app is in maintenance mode

[vaites]

The Artisan commands that process the queue jobs do not work in maintenance mode, but no message is displayed to indicate this. For example, the artisan queue:listen command displays the following message:

INFO Processing jobs from the [default] queue.

The problem is that even though the jobs are not actually processed. I know that this behaviour is documented here, but I suggest displaying a warning/error message if maintenance mode is active and only displaying the current one if the --force option has been used.

It would also be useful to show a flag or warning in the artisan queue:monitor command.

[shaedrich]

Additionally to the message that jobs are currently not processed, there should be a message when job processing is resumed.