Switch from Unoconv to LibreOffice and complete with alternatives

Switch from Unoconv to LibreOffice and complete with alternatives

Switch from Unoconv backed to directly use LibreOffice. Unoconv starts
to be buggy and LibreOffice is more tolerant to whether the server is
running, therefore Unoconv is rather in the way.

Use *pdftotext* for conversion of formats that will not convert to
text using LibreOffice (spreadsheets and presentations).

In case chache exists but input filename differ, then rename the
cached filename to match the input one. This is usefull for Mutt,
which always has a different temporary file.

Rename format "pdf" -> "zatura", cfr "emacs"