Fix PDF upload error not correctly handled when there is no HTTP response
In version 1.1.0 and before, when a PDF upload fails without an actual HTTP response, the PDF upload component would reach an invalid state and recover from it is only possible by a full page refresh.
This merge request changes the behaviour of the PDF upload component such that this does not longer break. It also makes the necessary front-end changes to ensure Quizzard compiles using the newest front-end libraries.
This fixes #57 (closed)