[Feature] Save Evaluation Results as PDF

[markusphil]

Now that we created some charts as results, we should also allow the admins to download them for further usage.

jsPDF seems to be the standard way for creating PDFs on the frontend.

https://stackoverflow.com/questions/47668546/generate-pdf-with-jspdf-and-vue-js
https://parall.ax/products/jspdf

I prepared a first, really basic implementation, but the document doesn't have any styling yet and the charts are missing.