添加导入、导出身份功能，目前导入到默认文件、从默认文件中读取

app/src/main/java/com/pkusz/min_vpn_client/activity/login/LoginActivity.java

@@ -12,6 +12,7 @@ import android.os.Bundle;
 import android.view.View;
 import android.widget.ImageView;
 import android.widget.TextView;
+import android.widget.Toast;
 
 import com.google.android.material.checkbox.MaterialCheckBox;
 import com.pkusz.min_vpn_client.GlobalSetting;
@@ -60,6 +61,8 @@ public class LoginActivity extends MINVpnBaseActivity<LoginActivityPresenter>
     private ClearAbleEditText etUsername;
     private CircularProgressButton btnLogin;
     private ClearAbleEditText etPassword;
+    private CircularProgressButton export_identity;
+    private CircularProgressButton import_identity;
 
     @Override
     protected void onCreate(@Nullable Bundle savedInstanceState) {
@@ -75,6 +78,8 @@ public class LoginActivity extends MINVpnBaseActivity<LoginActivityPresenter>
         etUsername=findViewById(R.id.etUsername);
         btnLogin=findViewById(R.id.btnLogin);
         etPassword=findViewById(R.id.etPassword);
+        export_identity=findViewById(R.id.export_identity);
+        import_identity=findViewById(R.id.import_identity);
 
         initView();
     }