Dynamically Promote Heading Levels

Would be nice if the importer promoted heading levels so that all headings always have a direct parent level. This is apparently quite a common issue on Wikipedia as people aren't encouraged to use a formal structure and articles start with H2 rather than H1.

In essence this would ensure articles start with H1 and have no missing headings between this and the lowest level.

Discussed further here: https://forum.xwiki.org/t/filter-streams-help-mediawiki-import/3586/8?u=ben.megson