Display better error messages from document processor (#243)

collector/scripts/watch/convert/as_docx.py

collector/scripts/watch/convert/as_markdown.py

collector/scripts/watch/convert/as_mbox.py

collector/scripts/watch/convert/as_pdf.py

collector/scripts/watch/convert/as_text.py

collector/scripts/watch/process_single.py

...Modals/MangeWorkspace/Upload/FileUploadProgress/index.jsx