add favorite contacts

src/app/app.component.html

src/app/app.component.ts

src/app/contact/contact-detail/contact-detail.component.html

src/app/contact/contact-detail/contact-detail.component.scss

src/app/contact/contact-list/contact-list.component.html

src/app/contact/contact-list/contact-list.component.scss

src/app/contact/contact-list/contact-list.component.ts

src/app/contact/contact.model.ts