Add option to choose multiple languages (easy on tesseract level, slightly tricky on GUI level)

Write to PDF as we go along, so memory requirements are reduced. Would require further modifying fpdf: https://github.com/jung-kurt/gofpdf/issues/110

We had reported (with video) a bug with permissions requests repeatedly being displayed on a new Mac, may be related to this: https://github.com/fyne-io/fyne/issues/2799

Maybe pay apple $100 for a certificate to avoid their security warnings (can be easily included in 'fyne package')

Add more tests.