Implement notification channel

app/src/main/res/values/strings.xml

@@ -5,6 +5,7 @@
   <string name="shortcut_start">Traccar - Start</string>
   <string name="shortcut_stop">Traccar - Stop</string>
   <string name="shortcut_sos">Traccar - SOS</string>
+  <string name="channel_default">Primary Channel</string>
   <string name="settings_id_title">Device identifier</string>
   <string name="settings_url_title">Server URL</string>
   <string name="settings_url_summary">Tracking server URL</string>