reference.odt:  Tidied styles.xml.
Moved fixDisplayMath from Docx writer to Writer.Shared.
OpenDocument writer:  Fixed RawInline, RawBlock so they don't escape.
ODT writer:  Use mathml for proper rendering of formulas.

Note:  LibreOffice's support for this seems a bit buggy.  But
it should be better than what we had before.