Edit document field `subject` (is newly implemented)

**How it works**

The field `subjects` is not displayed correctly, as its JSON structure has been reworked.

**How it should works**

The display of `subjects` is replaced by the new `subjects` in the document detailed view (public + pro):
    * `preferred_name`
    * `title` / `creator`
    * `term`
    * the subject type is displayed as tooltip
