New Html Metro styled report (Issue78)

Created new HtmlMetroReportBuilder.cs  for issue #78

Also an approval test for the expected HTML.

Used runtime T4 template to produce the Html as I already had the designed html skeleton. This approach also meant it was simpler to implement and lot less code as I didn't need all the helper methods such as "private HtmlReportTag OpenTag(string openingTag, HtmlTag tag)". I guess it would be possible to do all the reports (markdown etc) using this T4 approach.

I also added ConfiguredHtmlMetroReportTests.ConfiguringTheHtmlMetroReporterRunsWithoutError test to check it works when configured as part of an actual BDDfy test run, though I'm not sure if it's in the correct place or not...