Export participants to different formats

* CSV
* PDF (requires Python dependency `weasyprint`)
* ODS (requires Python dependency `pyexcel_ods3`)

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

priv/python/pdf.py

@@ -0,0 +1,4 @@
+from weasyprint import HTML
+
+def generate(html):
+    return HTML(string=html.decode('utf-8')).write_pdf()