Fix javascript.vm
XWIKI-8744: Introduce per wiki distribution status
* The distribution step templates are not found in my case if the path doesn't start with slash /.
XWIKI-8744: Introduce per wiki distribution status
* Use wiki syntax and fix deprecated call to $msg.get()
XWIKI-8744: Introduce per wiki distribution status
* Update the code that handles the step submit (step action).
* Remove the experimental warning message from the top of the distribution wizard steps.
* Apply a bit of code style.