Add ua selector

Support modify test url

Optimize android proxy

Fix the error that async proxy provider could not selected the proxy

lib/models/app.dart

@@ -34,6 +34,7 @@ class AppState with ChangeNotifier {
   List<Group> _groups;
   double _viewWidth;
   List<Connection> _requests;
+  num _checkIpNum;
 
   AppState({
     required Mode mode,
@@ -47,6 +48,7 @@ class AppState with ChangeNotifier {
         _viewWidth = 0,
         _selectedMap = selectedMap,
         _sortNum = 0,
+        _checkIpNum = 0,
         _requests = [],
         _mode = mode,
         _totalTraffic = Traffic(),
@@ -241,6 +243,15 @@ class AppState with ChangeNotifier {
     }
   }
 
+  num get checkIpNum => _checkIpNum;
+
+  set checkIpNum(num value) {
+    if (_checkIpNum != value) {
+      _checkIpNum = value;
+      notifyListeners();
+    }
+  }
+
   Mode get mode => _mode;
 
   set mode(Mode value) {