Add isOnline

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/BotImpl.kt

@@ -98,7 +98,11 @@ abstract class BotImpl<N : BotNetworkHandler> constructor(
         }
         _network = createNetworkHandler(this.coroutineContext)
 
-        _network.login()
+        while (true){
+            _network.login()
+            delay(3000)
+            logger.warning("Login failed. Retrying in 3s...")
+        }
     }
 
     protected abstract fun createNetworkHandler(coroutineContext: CoroutineContext): N

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/contact/QQ.kt

@@ -21,10 +21,15 @@ import net.mamoe.mirai.data.Profile
  * @author Him188moe
  */
 interface QQ : Contact, CoroutineScope {
+    /**
+     * 是否在线. 这个属性的值将会与服务器同步更新.
+     */
+    val isOnline: Boolean
+
     /**
      * 请求头像下载链接
      */
-   // @MiraiExperimentalAPI
+    // @MiraiExperimentalAPI
     //suspend fun queryAvatar(): AvatarLink
 
     /**