title: how to subscribe to action success callback using ngrx and effects
body: <p>I'm  trying to do simple thing - after some entity saved (using http request)
  I want to navigate back to list route. The problem is : how to subscribe to success action (or may be reducer or effect?)</p>
  
  <p>here is my actions code:</p>
  
  <pre><code>static SAVE_POST = '[POST] Save POST';
  savePOST(Post): Action {
      return {
          type: PostActions.SAVE_POST,
          payload: Post
      };
  }
  
  static SAVE_POST_SUCCESS = '[POST] Save POST Success';
  savePOSTSuccess(Post): Action {
      console.log('action: savePostSuccess')
      return {
          type: PostActions.SAVE_POST_SUCCESS,
          payload:Post
      };
  }
  </code></pre>
  
  <p>i'm using Effects:</p>
  
  <pre><code>   @Effect() savePost$ = this.update$
      .ofType(PostActions.SAVE_POST)
      .map(action =&gt; action.payload)
      .switchMap(post =&gt; this.svc.savePost(post))
      .map(post =&gt; this.postActions.savePOSTSuccess(post));
  </code></pre>
  
  <p>reducer:</p>
  
  <pre><code>const initialState: PostListState = [];
  
  export default function (state = initialState, action: Action): PostListState {
      switch (action.type) {
          case PostActions.LOAD_POST_SUCCESS: {
              return action.payload;
          }
          case PostActions.SAVE_POST_SUCCESS: {
              console.log('SavePOST SUCCESS',action.payload)
              let index = _.findIndex(state, {_id: action.payload._id});
              if (index &gt;= 0) {
                  return [
                      ...state.slice(0, index),
                      action.payload,
                      ...state.slice(index + 1)
                  ];
              }
              return state;
          }
          default: {
              return state;
          }
      }
  }
  </code></pre>
  
  <p>in my component i want to subscribe to success callback:</p>
  
  <pre><code>   handlePostUpdated($event) {
       this.post = this.code;
       let _post: Post = Object.assign({}, { _id: this.id, name: this.name, text: this.post });
       this.store.dispatch(this.postActions.savePOST(_post)); //not have "subscribe" method
  
    }
  </code></pre>
  
  <p>Thanks for Help</p>