fix broken html on admin overview
remove deprecated § handling

– § are now simply hidden
– they will become a normal character once all old questions have
  been updated to use the new syntax
– \emph handling has changed and is now fully supported everywhere
– math help has been updated accordingly. It now only shows the
  \( and \[ variants to start math, although $ and $$ will continue
  to work. Cmp. http://docs.mathjax.org/en/latest/tex.html#tex-and-latex-math-delimiters