Adds a check in the Admin Service to throw an error if the supplied configuration is empty or missing stageClass.

Adds exception handlers that return a JSON map of the error instead of dropping the user to the container's 500 error page.
A timeout in a processor now unconditionally restarts the system process

Also added test for a hanging stage that doesn’t respond to interrupts

Fixes #279
Extracts duplicated error response creation
Merge pull request #286 from remen/279_process_timeout

A timeout in a processor now unconditionally restarts the system process
Merge pull request #283 from laserval/admin-service-stage-config-attachment-fix

Adds check for empty configuration to Admin Service stage config endpoint