Byline rework

:construction_worker: Byline needs a rework to reduce code redundancy and make it easier to customize.

- [x] Writing byline tests.
- [x] Create files in opengever.base
- [x] byline.py baseclass
- [x] central byline.pt
- [x] update dossier
- [x] update repository
- [x] update document
- [x] update task

byline.pt
```html
<tal:repeat tal:repeat="item view/get_items"> 
  <li tal:attributes="class item/class" tal:condition="item/content">
     <span class="label"><span tal:content="item/label"></span>:</span>
     <span tal:condition="not: item/replace" tal:content="item/content"></span>
     <span tal:condition="item/replace" tal:replace="structure item/content"></span>
  </li>
</tal:repeat>
```