AthContainers: Adjust overload ordering to work better with python.

pyroot doesn't follow C++ rules for overload resolution. Instead, it tries calling methods in order and accepts the first one that works. This implies that if D derives from B and you you list foo(const B*) followed by foo(D*), you'll only ever be able to call the first of these from python even if you call it with a D instance. This can be avoided by reordering the method declarations.

This affects the setStore() methods. Reorder them so that we can call the non-const versions from python.