Affiliation: add a position attribute to the model
Author: add a position field to the model

Add a transient field affiliationPositions to the model,
 that can be used by the service class to define the n-to-m
 relationship between authors and affiliations.
serializer: adopt to model changes

AuthorFormat: reads and writes position and affiliations
AffiliationFormat: reads and writes  position
Assets: adopt test data to model changes model

Test data changed for Author and Affiliation
serializer: fix small bug in AuthorFormat.writes
serializer: adopt test
TestAll: add ConferenceCtrlTest
Merge pull request #66 from stoewer/master

Positions for abstracts and authors