New feature in export see #08862

- New feature #08862: More option in export heading
- New feature : allow to select another language when exporting
- Dev: add code+text, em code for code, length of abbreviated
- Dev: some change in question text
- Dev: todo : add some option in answer export
- Dev: todo : add plugin event (with list) ?

Not sure for the good manner to add exportHead event. Can do same than exportList, but maybe a global 'pluginList' can be a better solution. After set default: to call event with headType is easy.