[#6139] ticket:399 Improved Trac Wiki import scripts

* Copy the contents of the trac wiki home page to the Home page in the Allura wiki.
* Replace the wiki-toc div from trac with a Markdown [TOC] tag.
* Added the 'forgewiki.wiki_from_trac' ScriptTask that can do the export/import in one step
[#6139] ticket:399 Fix imports for ScriptTask
[#6139] ticket:399 Skip pages that can't be parsed (non-wiki)