TemplatingHttpHandler: use ParamsProvider as context

it can be dynamics whereas QHash<QString,QVariant> couldn't
MailSender: using QHash for headers rather than QMap

it is arguable to use either QMap or QHash in a full-featured e-mail
framework since headers can be multi-valued and their order may be of
some value along the e-mail lifetime, however MailSender only send a
mail at its very first hop
HtmlTableView: adding support for row anchor (<a name=> tag)