Implement method to merge actors
We need a method that allows to "merge two actors".
That means:
We have actor A and actor B and based on some findDuplicates
-mechanism these were identified as the same Actor.
The task is to reassign all roles of actor B in individual items (as contributor etc.) to actor B and then to eliminate actor B.
(notify: @stefan.probst, @cesare.concordia , @lbarbot, @matej.durco, @klaus.illmayer, @mkozak, @ekalata )