Frontend: fix typos

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Backend/Frontend: Fix: make it possible to run the OCR on PDF documents

Signed-off-by: Jerome Flesch <jflesch@gmail.com>
Main window: Don't display the various page orientations when only 1 is tried (when we redo the OCR or import an image)

Signed-off-by: Jerome Flesch <jflesch@gmail.com>