Resolve "Non determinism with tests involving the realign image function"

This MR fixes the non determinism in the tests by increasing the DPI from 72 to 150.

The MR implements and changes the following:

• Adds a new error message in the scan pipeline when not enough blobs are detected
• Use reportlab to generate blank PDFs instead of PIL
• Use correct position for student id widget
• Use a resolution of 150 dpi for the tests instead of 72 dpi
• Remove now unneeded upscaling of images
• Reduce noise for high noise test and now expect a success
• Clarify resample parameter for resizing
• Improve PDF flattening code in the scan tests
• Remove print statements
• Remove commented out code

Closes #326 (closed)