A mapping of IM protocol to an (unordered) set of IM addresses.
Each mapping is from an arbitrary protocol identifier to a set of IM addresses on that protocol for the contact, listed in no particular order.
There must be no duplicate IM addresses in each set, though a given IM address may be present in the sets for different protocols.
All the IM addresses must be normalised using ImDetails.normalise_im_address before being added to this property.
0.5.1