Byline rework

Byline needs a rework to reduce code redundancy and make it easier to customize.

  * Create files in opengever.base
  * byline.py baseclass
  * central byline.pt
  * update all byline.py with baseclass
  * update corresponding configure.zcml
  * remove unused byline.pt

byline.pt
```html
<li tal:attributes="class item/class" tal:repeat="item view/get_items">
      <span class="label" tal:content="item/label"></span>
      <span tal:condition="not: item/replace" tal:content="item/content"></span>
      <span tal:condition="item/replce" tal:replace="item/content"></span>
</li>
```