cleanup cs_spec.rb
add logger to client
refactor set_session_id - > session_id=
update readme
handle setting logger after creating the session
move parse_single_resource to Relation
refactor parse_single_resource on sensor_data_relation
refactor parse_single_resource of group_relation
remove uncessary default initialization
move get_single_resources to relation, refactor sensor_relation
refactor group_relation get_single_resource