added basic user group creation
do not serialize the subject owner relation details
add user_ip field to classification and remove user presence validation

Classifications can be submitted by non-logged in users, track these via the user_ip field.
include the set_member_subject_id in the set member subject serialiser

SetMemberSerialiser currently masquerades as a subject serializer for the overloaded subjects_controller#index. A classification requires the set_member_subject_id to be set for context of the Subject to SubjectSet.
remove :destroy and :update routes for Classifications
add classifications_controller create action
ensure consistent usage of subject_ids and names
add user_group create specs for location header and invalid params