Simplify new entity display

Followup on current development #733 (closed) after discussion with @kermorvant :

• use worker versions from TranscriptionEntity and not Entity
• only display one source of entity at a time (no mode where several worker versions are shown)
• add a mode to display no entities
• those modes should be switched using a <input type=radio> to view all possible values at once (instead of a select)
• remove entity validation