Indicate object links in 2D view

[dertseha]

In order to visualize object relationships, especially trigger chains, a line indication is requested.

Since this is an expensive search - as well as a mess to display all at once - it may be sufficient to only display the links from the currently hovered item.
Perhaps add a separate "type" of selection: Alt + click to mark one item as the focus item.

Tricky: objects that refer to either themselves, or objects in the same stack (at the same location)