Case T-577/16: Judgment of the General Court of 14 December 2017 — Campo and Others v EEAS (Civil Service — Officials — Agents — Remuneration — EEAS staff posted to a third country — Article 10 of Annex X to the Staff Regulations — Annual assessment of the allowance for living conditions — Decision reducing the allowance for living conditions in Montenegro from 15 % to 10 % — Plea of illegality)