[BUGFIX] Filepicker lacks support for file field (yet support inline only)

The FilePicker didn't support file fields but rather only inline fields.

Now it is detecting if the flex form field is a inline relation or file field and based on this another javascript function defined in the core´s formEngine is used to fill in form values.

Since the standard file field uses the files publicUrl as value we had to introduce a data-url attribute on imageViewHelper. Having this attribute on one of the links for a record is enough.