Genericity : remove legacy SILL config

This is a list of hard written linked to code.gouv.fr or SILL related config.

- [x] In `web/index.html` inside the `` it contains a lot of variable linked to gouv.fr and SILL (tracker, Twitter, Facebook)
- [x] There is a lot of variable with the name SILL inside.
- [ ] Inside the DB some variables have the name of a source : `SILLid`, etc

Start with web/index.html and review the checked legacy references in its head. Then locate the database schema or model definitions containing source fields such as SILLid; the work is complete when the remaining SILL or code.gouv.fr configuration references identified by the issue have been removed or updated.

Written by the indexing model from the issue text.