The main goal of this PR is to get rid of explorer_controller.js to unblock the migration to react-router. Previously we already used rxjs observables to migrate away from angular events. Observables were used to trigger actions to manage the react component's state as well as AppState. This PR builds upon this previous work. The actions already were done similar to redux, now the use of observables has been extended to use scan (see rxjs docs) which allows us to transform the actions into state updates.