JSON Form may crash when applied to elements not yet inserted in the DOM

[tidoust]

Code that enhance generated fields sometimes uses global selectors such as $(id), where id is an element generated by the underlying field. This works well provided the form element is in the DOM. However, JSON Form may very well be applied to an element that has not yet been inserted in the DOM (e.g. to prepare a view before rendering).

All selections in JSON Form should rather be scoped to node.el to guarantee that they parse the right subtree, no matter whether it is in the main DOM tree or not.

Similarly, the ACE editor receives "node.id" + "__ace" as initialization parameter. Internally, the ACE library uses getElementById to retrieve the element, which fails when the element is not yet in the DOM tree. The ACE editor should rather receive the element directly.