Improve preprocessing

[GenieTim]

Preprocessing has a few issues:

• too slow – make faster
• stop spaming "TempBarcodeCrop" (from barcodescaleresize) images
• log which files exactly failed to be processed

[GenieTim]

Currently, a few things could still be improved:

• speed up even more
• detect barcode / warn if default-template property is set wrongly
• improve resilience even further