Forum themes are using vendored copy instead of inheritance

[kkremitzki]

The FreeCAD and FreeCAD-Dark forum themes use a vendored copy of an upstream phpBB theme from an old version; the current version of phpBB has diverged from this copy, resulting in display issues. Instead of using a copy, these themes should use inheritance from the base theme, with the changes specific to our variant listed out directly, rather than existing as direct modifications to the theme's files. This is the proper fix to existing issues, and will result in more resilience to further upstream changes in future phpBB versions.

Reference: https://www.phpbb.com/styles/create/

[yorikvanhavre]

I think we should remove these custom themes entirely as they are totally out of sync with current phpBB...
And then redo some themes the proper way, by just overriding the needed files...

[hasecilu]

My main reason to use the custom themes was the dark mode, using "Dark Reader" extension takes care of this regard, the little icons on top to redirect to come FreeCAD sites would be nice to have them re-implemented, the ddg search is not a must have for me, the default onsite search works pretty good also.