Editable scaffolder HTML

[mdutoo]

Make the HTML generated by scaffoldingProxy editable when in new "editable" (vs for now only "dynamic") mode.

First complete the spec below, then do it.

How to do that - ex. in node / connect :

• let node / connect save in a web dir the generated html when going to "editable" mode and redirect to it rather than to the dynamic scaffoldingProxy when there is such a page in the web dir.
• Add in the velocity template a "make editable/revert to generated" toggle button, and in editable model "save" and "cancel" buttons, all pointing to connect-implemented web actions.

[JGuillemotte]

First thing done : The generated html form send a JSON data structure. It is now possible to add new features easilly to the form.