Fix MQTT implementation, align with DStarGateway, and add documentation

MQTT Implementation (aligned with DStarGateway / MMDVMHost):
- Rewrite MQTTConnection with mosquitto_loop_stop() fix to prevent
  background thread zombies on shutdown
- Add MQTT authentication support (mqttAuth, mqttUsername, mqttPassword)
- Add configurable client name (mqttName) used as topic prefix
- Use PID-based client IDs (avoids time_t truncation on 32-bit ARM)
- Use std::string interface throughout (no wxString in MQTT layer)
- Align JSON link status fields with DStarGateway (repeater/reflector/
  protocol/reason/action) for dashboard compatibility

Shutdown Safety:
- Add MQTTLogFinalise() calls to both daemon (IRCDDBGatewayAppD::run)
  and GUI (IRCDDBGatewayApp::OnExit) shutdown paths to ensure clean
  MQTT disconnection and thread cleanup before process exit

JSON Status Events:
- Update all ~30 WriteJSON call sites across DPlus, DExtra, DCS, and
  CCS protocol handlers to use new function signatures
- Simplify IRCDDBGatewayThread::writeJSONStatus to delegate to
  WriteJSONStatus

Config Parser Hardening:
- Add empty-line crash guard to IRCDDBGatewayConfig, TimerControlConfig,
  and TimeServerConfig parsers (str.IsEmpty() check before GetChar)

Documentation:
- Add MQTT.md with topic structure, JSON examples, and troubleshooting
- Add CONFIGURATION.md with full reference for all config files
- Add BUILD.md with build parameters and dependency information
- Add linux/ example configs for ircddbgateway, timeserver, timercontrol
- Modernise README.md with feature list and DStarGateway recommendation

TimerControl/TimerControlConfig.cpp

@@ -109,7 +109,7 @@ m_y(DEFAULT_WINDOW_Y)
 	wxString str = file.GetFirstLine();
 
 	while (!file.Eof()) {
-		if (str.GetChar(0U) == wxT('#')) {
+		if (str.IsEmpty() || str.GetChar(0U) == wxT('#')) {
 			str = file.GetNextLine();
 			continue;
 		}