Support variation of HTML5 signature:

<!DOCTYPE html SYSTEM "about:legacy-compat">

This is an alternative for HTML generators that don't support DOCTYPE html.  XSLT is an example of such a generator.
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Updated: Whatsnew.htm
Lazarus print support
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Lazarus print support
Fixed: bad typecast / wrong arguments passed to GetImageMask()
Merge branch 'HtmlViewer-11.4-to-11.5' of https://github.com/BerndGabriel/HtmlViewer into HtmlViewer-11.4-to-11.5
Implementation of Meter tag
Updated class_hierarchy with TMeterObj
Fixed: Block content section must not get class name and id of the block.
Moved: "IDEXPAND_" handling from HotSpotTargetClick to THtmlViewer.URLAction
Changed: GetActiveBase()/GetActiveTarget() to GetViewerBase(Vw:THtmlViewer)/GetViewerTarget(Vw:THtmlViewer)
Fixed: Issue 181: Gifs are not animated, if there are too many on the same page