Behavior

only displayed when an object has image/audio/PDF/video or book data
when an object has multiple data types, tabs are shown (s. below):
- the tabs are centered
if there are multiple object elements in one tab: pagination below the object
- in mobile, they should be swipe-able
in the Viewer, the object is always placed in a invisible image area, in which the image can be zoomed or moved
- this guarantees that the size of the Viewer does not change with the size of the object
- it also makes sure the distance to the red area remains the same
  - the distance between image and red area should always be 20 px

Changes:

Tabs:

Viewer: