Include cron args in wp cron event list

When scheduling a cron event, you can supply args which will be serialized and then passed to the hook function when it is run. When doing `wp cron event list`, however, there is no `args` column, and so there is no way to tell the difference between multiple events scheduled for the same hook (but with different args).

Granted, the args may be large, so perhaps it should be an optional field to display. Displaying it as PHP-serialized data seems fine, and perhaps the only reliable option.

Relates to #1336.