Missing PDFs in the test environment cause an explosion in log output (2)

Currently, some PDF files are missing on which some Selenium tests depend. This generates an incredible amount of stack traces as every API call to download a pdf now results in a lengthy stacktrace. Quizzard does not expect its PDF folder to ever get out of sync with its database, as it means someone has been tampering with the PDF folder (which is also what happend here), however this may actually happen in production too. I think two things should be done here:

• Make the PdfFileService print a much more concise message when a PDF is missing (still log it as [SEVERE])
• Restore the missing PDF files
• Copy the PDFs to the target folder
• Remove redundant PDFs