add shell platform back and add support for job.credentials back for email

hi!

still trying to get these to work, but it's two things i need: shell access, and setting the credentials in the job, apparently, to keep email.michiel.5apps.com working, my app doesn't send the credentials in the register command.

which app are you using to send email, do you have it public somewhere? then i can see how you set the credentials.