Fix validation/display of unknown workflow automation chains used in transitions

When an AutomationChain is defined in a workflow transition, after being deleted, no validation error is thrown. When the workflow is validated, only the input and ouput chains of a node are checked. The chains on transitions should be checked too.

Steps to reproduce :

• create an automation chain
• create a workflow and on a node, create a new transition using the automation chain created before
• delete this chain

=> there is no validation error about this