Add option to add signature

eidesstattliche_erklaerung.tex

@@ -13,7 +13,11 @@ to another academic institution and has also not yet been published.
 \>Karlsruhe, \theThesisSignatureDate
 \end{tabbing}
 
-\vspace{2cm}
+\ifx\theThesisSignature\empty
+  \vspace{2cm}
+\else
+  \hspace*{1.5em}\includegraphics[height=\theThesisSignatureHeight]{\theThesisSignature}
+\fi
 \begin{tabbing}
 \hspace{3em}\= \kill
 \>\theThesisAuthor\\[1ex]
@@ -39,7 +43,11 @@ Ich habe keine anderen als die angegebenen Quellen und Hilfsmittel benutzt und w
 \>Karlsruhe, den \theThesisSignatureDate
 \end{tabbing}
 
-\vspace{2cm}
+\ifx\theThesisSignature\empty
+  \vspace{2cm}
+\else
+  \hspace*{1.5em}\includegraphics[height=\theThesisSignatureHeight]{\theThesisSignature}\\[0.5ex]
+\fi
 \begin{tabbing}
 \hspace{3em}\= \kill
 \>\theThesisAuthor\\[1ex]