Add caption font size option in Nina-report

[jenast]

The font size of the caption is hard-coded. We could add an option to change this.
The relevant portion of the template.tex

%\usepackage[font=it,format=plain,labelfont=bf,justification=justified,singlelinecheck=false,labelsep=period]{caption}
for example with scriptsize font.
\usepackage[font={it, scriptsize},format=plain,labelfont=bf,justification=justified,singlelinecheck=false,labelsep=period]{caption}

To-do: make a caption_fontsize parameter in the template and insert it into the template.tex