Persist automation scripts in separate JS files

Automation scripts are currently saved in XML format

It makes it hard to develop an automation in an useful IDE using direct git access.
Especially due to the escape sequences ( " etc. ).

TO DO:

• Keep both loading method : external JS file and XML
• Persist in external JS file on new save
• Write it back in XML inside the Nuxeo contribution (ask platform if they can add the external JS file feature in the contribution ?)
• Beware of encoding !