Added paragraph symbol font (Get/SetSymbolFont in attribute)

Added paragraph symbol font (Get/SetSymbolFont in attribute)
and use this font instead of paragraph font if specified.

wxRichTextBuffer::SetStyle extended to respond to flags for
specifying undo, optimization (only apply the style necessary
for display when content/base/paragraph attributes are combined),
and para/character styles only.

wxRichTextBuffer::GetStyleForRange gets the common attributes
for a range, e.g. for showing common attributes in a formatting
dialog.

Implemented Roman numeral bullet points.

Fixed wxRichTextImage copy bug.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41704 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775