Move source icon in incident detail to the header

[nilmerg]

Objects are tied to single sources by now. There's no reason to show the source icon for every history entry anymore.

But since it's tied to the object, it should instead be shown in the header alongside the object's name. (i.e. Aligned right, as previously)

A beneficial side effect should be, that the icon is also visible in the primary incident list from there on.