MBS-5813: In the release editor, show the 'artist editable' checkbox

c2848355 (MBS-5740) made this checkbox only appear conditionally, if
the table contained <input> elements with type="checkbox", at the
time of initialization. However, the release editor dynamically creates
checkboxes, and so the select all checkbox would not be shown. This
commit simply re-shows the checkbox in the release editor.