Multiple style blocks in output

[CharliePoole]

The V3 reports (some or all, not sure) contain a <style> element in the template, with the result that the styles are repeated for each input file, even when the output is going to a single file.

We should first decide if we really want to embed a style in the file. If we do, then it may have to be handled programmatically in C# rather than in the template. It could be written or not based on the setting of the NoHeader option just as the html header is now handled.