SoftEffector that respects existing Constraints

[nassosy]

This is a modified version of the "Soft Effector Operator" by "(c) Andrew Nicholas 2006"
I changed it so that it can be applied to complex Rigs with constraints
Instead of ignoring them, it moves constraints (if any) that affect position from the Effector to the created SoftEffector Null
I haven't heavily tested it, so use it at you own risk.