Swap Map and Panorama

[Kletterer]

User story

1. As a user
2. I want to swap the map and the panorama
3. So that the map can be shown in the "main window"

Acceptance criteria

• there is a swap button displayed near the small window.
• hitting the swap button twice results in the same "configuration" as before (e.g. starting from the panorama being displayed in the main window, after hitting the swap button twice, the panorama is displayed in the main window again)
• the class ViewerState is implemented as described in the API documentation and updated accordingly.

Definition of done

• Code has been peer reviewed
• Documentation has been updated
• Code has been included into the release (candidate)
• No syntax / runtime errors
• Code is well structured and formatted