Merge pull request #3578 from jakobgager/latex_image_handle

Use adjustbox to specify figure size in nbconvert -> latex

Instead of hardcoding the image size used when compiling latex, a maximum size is specified only.
This way smaller images don't get enlarged. The Sphinx converter use the same approach.

IPython/nbconvert/templates/latex/base.tplx

@@ -41,14 +41,14 b' it introduces a new line'
 
 ((*- block data_png -*))
 \begin{center}
-\includegraphics[width=0.7\textwidth, height=0.9\textheight, keepaspectratio]{(((output.key_png)))}
+\includegraphics[max size={0.7\textwidth}{0.9\textheight}]{(((output.key_png)))}
 \par
 \end{center}
 ((*- endblock -*))
 
 ((*- block data_jpg -*))
 \begin{center}
-\includegraphics[width=0.7\textwidth, height=0.9\textheight, keepaspectratio]{(((output.key_jpeg)))}
+\includegraphics[max size={0.7\textwidth}{0.9\textheight}]{(((output.key_jpeg)))}
 \par
 \end{center}
 ((*- endblock -*))
@@ -144,6 +144,9 b' unknown type (((cell.type)))'
 \usepackage{ucs}
 \usepackage[utf8x]{inputenc}
 
+% Scale down larger images
+\usepackage[export]{adjustbox}
+
 %fancy verbatim
 \usepackage{fancyvrb}
 % needed for markdown enumerations to work