Provide more widget presentation options

Some widgets, especially list and complex widgets, are often rewritten to be able to
control the overall presentation of the list/map of values presented.

The default list widget currently presents a table, using one row per subwidget, the
first column presenting the subwidget label, and the second on the subwidget value
or input (in edit mode). There should be options (widget properties would be
enough) to:

• get rid of the first column presenting the label, especially when there is only one
  subwidget (for a list of names for instance)
• present widget labels as table headers, instead of using the first column for that
• present joined values as one text (values joined by a special character ",",
  finished by another character or message "# {messages['label.and']}

  for
  instance).

• add divs that may help with CSS styling of the page.

The same configurability could be added to complex widgets (presenting maps, and
currently using a rendering similar to the list widget).

There is also a bug happening when all widgets of a row are "hidden": the row is still
rendered, which makes it possible to break rendering (needs to be verified and
selenium tested).