UNIQUE_ID_OFFSET [int]:
{@link Target}s and {@link TargetPedestrian}s share the same address space for ids!
This can cause conflicts when the target potential is retrieved
in "PotentialFieldTarget.getPotential()". "PotentialFieldTarget"
stores potentials in a map. Therefore, use
a fixed offset to discriminate {@link Target}s and {@link TargetPedestrian}s.