Introduced a Opertaion enum that is passed to each call of WeightFunction#weight

This allows dedicated weight calculations per operation. In certain
circumstance it is more efficient / required to ignore certain factors in the weight
calculation to prevent for instance relocations if they are solely triggered by tie-breakers.
In particular the primary balance property should not be taken into account if the delta for
early termination is calculated since otherwise a relocation could be triggered solely by the
fact that two nodes have different amount of primaries allocated to them.

Closes #2984