AthContainers, etc: Update swap to work on AuxVectorData.

Update the swap method of IAuxTypeVectorFactory / AuxTypeRegistry to take AuxVectorData instances rather than bare pointers. Remove the swap static method from AuxTypeVector. Also alter swap to operate on a range, rather than a single pair of elements.

Refactoring to make possible dependencies between auxiliary variables, as would be used to support packed links / jagged vectors.