modification: fix action menu
- modification.py: run_pdfstruct when toc not present; action menu on "Visualisation" when pdf is selected; add legend for titles; buttons for both actions;
- utils.py: add receive_file, tested and used by st_utils.receive_files
- update streamlit-option-menu to v0.3.6
- move to liriae-common v0.9.0: use PdfFile.get_titles and Submission.get_titles; drop get_pdf_toc, get_final_toc