Kann ich die Section-/Subsection-Nummern in die Beamer-Headline einfügen?

\documentclass[12pt]{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\usepackage{libertine}
\usepackage[libertine,liby,slantedGreek]{newtxmath}

\usetheme{AnnArbor}
\usecolortheme{beaver}
\usefonttheme{professionalfonts}
\setbeamertemplate{navigation symbols}{}

\setbeamertemplate{headline}% Definition aus beamerouterthemeinfolines.sty geändert
{
  \leavevmode%
  \hbox{%
  \begin{beamercolorbox}[wd=.5\paperwidth,ht=2.65ex,dp=1.5ex,right]{section in head/foot}%
    \usebeamerfont{section in head/foot}\thesection\ % Hier geändert!!!
    \insertsectionhead\hspace*{2ex}
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.5\paperwidth,ht=2.65ex,dp=1.5ex,left]{subsection in head/foot}%
    \usebeamerfont{subsection in head/foot}\hspace*{2ex}\thesection.\thesubsection\ % Hier geändert!
    \insertsubsectionhead
  \end{beamercolorbox}}%
  \vskip0pt%
}

\setbeamertemplate{footline}
{
  \leavevmode%
  \hbox{%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,left]{date in head/foot}%
    \usebeamerfont{date in head/foot}\hspace*{1em}\insertshortauthor
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.3333335\paperwidth,ht=2.25ex,dp=1ex,center]{date in head/foot}%
    \usebeamerfont{date in head/foot}\inserttitle
  \end{beamercolorbox}%
  \begin{beamercolorbox}[wd=.333333\paperwidth,ht=2.25ex,dp=1ex,right]{date in head/foot}%
    \usebeamerfont{date in head/foot}\insertframenumber{} / \inserttotalframenumber\hspace*{1em}
  \end{beamercolorbox}}%
  \vskip0pt%
}

\setbeamerfont{frametitle}{size=\large}

\title{Titel}
\author{Tom}

\begin{document}
\section{Thema A}
\subsection{Unterthema B}
\begin{frame}
  \frametitle{Frametitel C}
  Text
\end{frame}
\end{document}