refactor(plan-editor): remove unused imports

fix(plan-editor): fix precondition in `createActivity`

feat(app): display notifications as popup

feat(header): add notifications button

feat(notification-popup): implement `NotificationComponent`

feat(notification-panel-button): Implement `NotificationPanelButton`

feat(notification-panel): implement `NotificationPanelComponent`

fix(post-comment): reset form after submit

feat(notification): implement `NotificationService`

feat(intersection-observer): allow disabling observer

refactor(intersection-observer): remove console log

fix(environment): update env files

feat(intersection-observer): implement `IntersectionObserverDirective`

feat(messaging): only reinitialize when user id changes

fix(messaging): shareReplay bus to ensure it is the only instance