Utiliser le setting appName à la place de "LaBoîte" dans les traductions

Cf. sondage!169 (merged)

laboite-blog-front$ rgrep LaBo.*te 
src/components/navigation/Nav.svelte:      <img src="/Leblog.png" alt="LaBoite - Blog" />
src/utils/theme/index.scss:// LaBoite brand colors
src/utils/locales/fr.json:      "developped": "Le Blog est un service du portail LaBoite sous licence",
src/utils/locales/en.json:      "developped": "Le Blog is an application from LaBoite licensed as",