v8.3.0 New features: * Slow mode (#192): * new option in room configuration to set the slow mode duration (new prosody module mod_muc_slow_mode). * default duration is configurable in channel's chat rooms options. * backend rejects messages when the slow mode is not respected. * front-end: display an infobox when slow mode is active. * front-end: disable the message field during the slow mode duration. Minor changes and fixes: * Fix ConverseJS build: translations were missing, and only english was available. * Replaced a sync file operation by an async one, to avoid blocking the server. * Fix ConverseJS bug: room information not correctly refreshed when modifications are made by other users. * Translation update: German, French.