add auto update subscriptions with interval

V2rayNG/app/src/main/kotlin/com/v2ray/ang/AppConfig.kt

@@ -87,4 +87,11 @@ object AppConfig {
     const val MSG_MEASURE_CONFIG = 7
     const val MSG_MEASURE_CONFIG_SUCCESS = 71
     const val MSG_MEASURE_CONFIG_CANCEL = 72
+
+    // subscription settings
+    const val SUBSCRIPTION_AUTO_UPDATE = "pref_auto_update_subscription"
+    const val SUBSCRIPTION_AUTO_UPDATE_INTERVAL = "pref_auto_update_interval"
+    const val DEFAULT_UPDATE_INTERVAL = "1440" // 24 hours
+    const val UPDATE_TASK_NAME = "subscription-updater"
+
 }