Merge branch '428-moteur-de-recherche-sur-la-page-d-accueil' into '60-ajout-de-la-fonctionnalite-respect-des-criteres'

Resolve "Moteur de recherche sur la page d'accueil"

See merge request !103

+ Corrections in English documentation

Refs #428

toggle search field by clicking a search icon in the nav bar
use flex for search field

multiple terms search: all terms must match
added empty descriptions in language files for each module

move icon files into right folder
fix language code detection for more than 2 letters codes