Unify contactdata and socialmixr #2
Description
I think the two packages fill 2 different niches and it's good to keep them both alive (especially since both of them are already on CRAN).
However, we should make sure that they play well together and that it is easy for users to go from one to the other.
It might also be useful to provide a shared S3 class for contact matrices so we can write common methods.
See also: epiforecasts/socialmixr#55