us-390_Improve connect page

src/app/user/components/auth/login/login.component.html

src/app/user/components/auth/login/login.component.scss

src/app/user/components/auth/login/login.component.ts

src/assets/img/connexion_illu.svg

src/i18n/messages.en.xlf

src/i18n/messages.fr.xlf

src/scss/variables.scss