Added unit test for SafeHtmlValidator
Footnote only allowed on Publication HtmlAttachments

Commit also modifies SafeHtmlValidator to set @record instead
of passing it round as method arguments.
Footnotes are styled
Govspeak help includes footnotes where appropriate
Publication doesn't allow footnotes in body
Require govspeak version ~> 0.2.4

Because that version allows sanitize version 2.0.6