Move math style to FontInfo and compute the font sizes for scriptstyle and
scriptscriptstyle according to standard proportions: 0.73 and 0.55.
This is simpler and more accurate. It also fixes the font size of
${\scriptscriptstyle {\textstyle A}}A$ which exposed the limitations of the
previous approach.
WriteStream is now built from an otexstream instead of an odocstream, and
therefore counts lines in a TexRow. Calls to TexRow are added in relevant places
in math insets.
This finishes adding line tracking for math in the source panel and for forward
search.
