syncLang.py: improvements

[mlep]

Following comments in PR #3179, here are ideas for improving syncLang.py:

• automatically generate the translation status with each push to master and publish a html version on jabref.org
• keep a constant order for the table of languages: English first, then alphabetical (or all alphabetical). (I guess it currently depends on the OS)
• put the table of menus first (so that is it not discouraging newcomers with a huge number of strings waiting for translation).
• align to the right the columns with numbers (easier to read, but just a tiny detail).

[LinusDietz]

• Update to python3
• Apply object-oriented design principles

[LinusDietz]

Successor Issue: https://github.com/JabRef/help.jabref.org/issues/171