add filter dropdown in news, link visits to backend, improve auth service

oser-app/src/app/app-routing.module.ts

oser-app/src/app/app.module.ts

oser-app/src/app/core/auth/auth.service.ts

oser-app/src/app/core/index.ts

.../src/app/showcase-site/news-page/news-page.component.html

.../src/app/showcase-site/news-page/news-page.component.scss

...pp/src/app/showcase-site/news-page/news-page.component.ts

oser-app/src/app/showcase-site/shared/article.service.ts

oser-app/src/app/ui/index.ts

oser-app/src/app/ui/login/login.component.html

oser-app/src/app/ui/login/login.component.scss

oser-app/src/app/ui/login/login.component.spec.ts

oser-app/src/app/ui/login/login.component.ts

oser-app/src/app/ui/ui.module.ts

oser-app/src/app/visits/shared/schema.config.json

oser-app/src/app/visits/shared/schema.ts

oser-app/src/app/visits/shared/visit.model.ts

oser-app/src/app/visits/shared/visit.service.ts

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

oser-app/src/app/visits/visits-routing.module.ts