Workflow.py: fix that transition can have single script defined; add a missing function wrapWorkflowMethod.

erp5_workflow: for the sake that workflow view transition/interaction don't show related scripts list correctly; and interaction's trigger methods list doesn't show correcly.

Workflow.py: fix that transition can have single script defined; add a missing function wrapWorkflowMethod.

erp5_workflow: for the sake that workflow view transition/interaction don't show related scripts list correctly; and interaction's trigger methods list doesn't show correcly.

This is still a work in progress

This will ease debugging from posted test results.
This code should be synchronous (no Blob asDataURL method for example) and so, btoa is used.

Sadly, btoa will fail with unicode character
Do not report HTML error in such case, until a cleaner dataURL is implemented