Fix hot reload of changes in workflow configuration

Steps to reproduce:

• Create a simple workflow in Studio, available on certain document types with an assignee.
• Hot reload the project to Nuxeo.
  => Workflow functions as expected.
• Modify the workflow in Studio, changing:
  • the type of document on which it is possible to start the workflow
  • the workflow label
  • the assignee
• Hot reload the project to Nuxeo.
  => Workflow is available on the new document type
  => Label has not changed
  => Assignee has not changed

Looking at the workflow zip in the studio package bundle, all of the changes are present, however, they are not taken into account in Nuxeo because workflows are only read during server start/stop.