add presentations/esup-days-18-smsu-v2: start with empty reveal.js presentation customized for esup

the default simple theme css/theme/source/simple.scss changes:

$mainFont: 'Arial', sans-serif;
$headingFont: 'Arial', sans-serif;
$linkColor: #FF6600;
presentations/esup-days-18-smsu-v2: alpha version