Implement Tags as standard feature in XWiki

Implemented Simple Tag Feature using standard XWiki Objects

• a preferences should activate tags
• the keywords should be stored in a StaticListClass in relational mode in 'input' display mode
• the keywords selection should be available in edit mode (wiki and wysiwyg) and in inline mode (#set($showtags=0) should deactive showing tags)
• tags should be displayed in the Attributes Panel (with parent and other data)
• a Javascript selection should allow to choose from list of tags (defined in the ListClass)
• RSS feeds should be available for each tag