Put default font family and size behind a message so the registerd NTIHTMLReader subclass can customize it. Use Open Sans 14.0 if no font is specified when parsing html.
When writing html use the same default font family and size that the reader uses.  When writing font-family out use the family not fontName.  Often those are different.
Empty NTIEditableFrames default to the same default font family and size that the reader and writer use.  When we set an attributed string, if there is no font specified (presumably because we came from a raw string) apply the default font.