Add SelectWidget formatting options to AutocompleteWidgets

Problem/Motivation

The SelectWidget has options to display Name, NativeName and ISO code.
The AutocompleteWidget has not.

This might be added.

Steps to reproduce

set settings for SelectWidget, that do not exist for Autocomplete widget.

Proposed resolution

Remaining tasks

- let SelectWidget inherit from StringTextfieldWidget, not WidgetBase;
- let AutocompleteWidget inherit from SelectWidget, not StringTextfieldWidget;
- adapt AutocompleteController, so it gets either the widgetsettings, or the list of possible Values. (thisis the hardest part)
- remove the TextfielWidget options from the SelectWidget settingsform, by checkin exact class.

User interface changes

User can now also select from native name.

API changes

Data model changes