Some small, not necessarily visible improvements to websites

Duplication of «news» posts to the category «Announcement and Communication» (called companion post) is now done by parsing RSS rather than rendered HTML, to avoid glitches.

The script that automatically creates the companion post in forum (and embed comments) is no more active in preview mode (in blog side), still to avoid weird behaviours.

And the categories in dropdown menus are reorganized, it was a true mess :joy_cat: