Allow input file (multiple uploads) to be used outside of shadow forms.

[Aldus83]

At the moment, the [INPUT|type=file] field, being used for drag & drop / multiple file uploads, can only be used inside a Shadow form.
This happens because the javascript needed by this input is loaded inside an invisible shadow tab:

https://github.com/quantacms/quanta/blob/master/engine/modules/core/node/tpl/node_data.inc

We need to make this more consistent, so that:

• the JS is loaded when there is an actual [INPUT|type=file], independently from where it's called
• the JS is never loaded two times