Finally the solution to affiliations problem.

Now both presenter and authors have a many to many relationship with
affiliations. This is all right for authors while for presenter this
should be more like one-to-many relationship because for a given session
there can only be one presenter which is actually the profile of the
currently logged in user. But this would not allow easy integration of
affiliations choose field in the edit profile form.
Also now affiliations have a ForeignKey to User in order to narrow down
and show only those affiliations that are of interest to current user
and its abstract.