commentfield.vm should not manipulate the XWikiComment class

commentfield.vm is in charge of generating a new editor field on demand for the comments.
It needs to take into account the wiki and user editor preferences as well as the settings of the XWiki.XWikiComments.comment field for its rendering
In addition, in case of error when submitting a captcha, or when editing a comment, the submitted content must be displayed again to the user.
The current approach of the script is based on XClass manipulation that

• complex
• can cause strange race conditions

It's easier to directly use the edit script services to generate editors matching the requirements listed above.