Created a utility function for OK results, ts_api:make_json_200/2
Created ts_common:new/1 and ts_common:update/1 to generalize record creation and update.
Refactored ts_timeline:new/1 and ts_timeline:update/1 to use the ts_common functions.
Implemented ts_json:record_to_ejson/1 and ts_json:ejson_to_record/1 for ts_user records.
Implemented ts_user module.