add showTopic() - Allow to programmatically select a topic

So far, all selects were initiated by the user by traversing the tiles.
Now, we'd like to select a given topic from outside, e.g. from content.
We need to
1. find the topic based on title or ID
2. possibly create new topics
3. create screen objs for the topic and its parents,
   because it may not be on screen and created yet
4. highlight the parent objs until root
5. select this obj

TODO Step 4/5 are still buggy