support stacking dialogs

electrum/gui/qml/components/controls/ElDialog.qml

@@ -9,9 +9,9 @@ Dialog {
 
     onOpenedChanged: {
         if (opened) {
-            app.activeDialog = abstractdialog
+            app.activeDialogs.push(abstractdialog)
         } else {
-            app.activeDialog = null
+            app.activeDialogs.pop()
         }
     }
 }

electrum/gui/qml/components/main.qml

@@ -27,7 +27,7 @@ ApplicationWindow
 
     property alias stack: mainStackView
 
-    property Dialog activeDialog: null
+    property variant activeDialogs: []
 
     header: ToolBar {
         id: toolbar
@@ -228,8 +228,9 @@ ApplicationWindow
     }
 
     onClosing: {
-        if (activeDialog) {
+        if (activeDialogs.length > 0) {
             console.log('dialog on top')
+            var activeDialog = activeDialogs.pop()
             if (activeDialog.allowClose) {
                 activeDialog.close()
             }