Make it easier to merge entities from two different searches

[andreasvc]

When correcting coreference output from a system, it often happens that two entities need to be merged. This is already possible, but it's a bit awkward to find them if they don't have a keyword in common:

• User searches for entity A, selects A
• User searches for entity B, but meanwhile selection A is no longer visible, so cannot verify if it's correct, or the selection is accidentally lost (wrong keypress or click) ...

I don't know the best way to solve this. Maybe 2 search bars?