Properly handle modal pages

This fixes various page flow issues when opening multiple of those.

src/app/LocationPicker.qml

@@ -27,7 +27,7 @@ Kirigami.Page {
         text: i18n("Pick Location")
         onTriggered: {
             coordinate = map.center;
-            applicationWindow().pageStack.pop();
+            applicationWindow().pageStack.goBack();
         }
     }
 

src/app/SettingsPage.qml

@@ -54,7 +54,7 @@ Kirigami.ScrollablePage {
             Kirigami.FormData.isSection: true
             text: i18n("Favorite Locations")
             icon.name: "go-home-symbolic"
-            onClicked: applicationWindow().pageStack.push(favoriteLocationPage);
+            onClicked: applicationWindow().pageStack.layers.push(favoriteLocationPage);
         }
 
         // Online services
@@ -90,7 +90,7 @@ Kirigami.ScrollablePage {
             Kirigami.FormData.isSection: true
             text: i18n("Public Transport Information Sources...")
             icon.name: "settings-configure"
-            onClicked: applicationWindow().pageStack.push(ptBackendPage)
+            onClicked: applicationWindow().pageStack.layers.push(ptBackendPage)
         }
 
         QQC2.Switch {

src/app/WelcomePage.qml

@@ -48,7 +48,7 @@ Kirigami.ScrollablePage {
 
         QQC2.Button {
             text: i18n("Got it!")
-            onClicked: applicationWindow().pageStack.pop();
+            onClicked: applicationWindow().pageStack.goBack();
             Layout.alignment: Qt.AlignRight
             visible: ReservationManager.isEmpty()
         }

src/app/main.qml

@@ -79,7 +79,8 @@ Kirigami.ApplicationWindow {
                 id: statsAction
                 text: i18n("Statistics")
                 iconName: "view-statistics"
-                onTriggered: pageStack.push(statisticsComponent)
+                enabled: pageStack.layers.depth < 2
+                onTriggered: pageStack.layers.push(statisticsComponent)
             },
             Kirigami.Action {
                 id: healtCertAction
@@ -87,15 +88,17 @@ Kirigami.ApplicationWindow {
                 iconName: "cross-shape"
                 onTriggered: {
                     healtCertificateComponent.source = "HealthCertificatePage.qml"
-                    pageStack.push(healtCertificateComponent.item)
+                    pageStack.layers.push(healtCertificateComponent.item)
                 }
+                enabled: pageStack.layers.depth < 2
                 visible: HealthCertificateManager.isAvailable
             },
             Kirigami.Action {
                 id: settingsAction
                 text: i18n("Settings...")
                 iconName: "settings-configure"
-                onTriggered: pageStack.push(settingsComponent)
+                enabled: pageStack.layers.depth < 2
+                onTriggered: pageStack.layers.push(settingsComponent)
             },
             Kirigami.Action {
                 text: i18n("Export...")
@@ -105,19 +108,22 @@ Kirigami.ApplicationWindow {
             Kirigami.Action {
                 text: i18n("Help")
                 iconName: "help-contents"
-                onTriggered: pageStack.push(welcomeComponent)
+                enabled: pageStack.layers.depth < 2
+                onTriggered: pageStack.layers.push(welcomeComponent)
             },
             Kirigami.Action {
                 id: aboutAction
                 text: i18n("About")
                 iconName: "help-about-symbolic"
-                onTriggered: pageStack.push(aboutComponent)
+                enabled: pageStack.layers.depth < 2
+                onTriggered: pageStack.layers.push(aboutComponent)
             },
             Kirigami.Action {
                 id: devModeAction
                 text: "Development"
                 iconName: "tools-report-bug"
-                onTriggered: pageStack.push(devModePageComponent)
+                enabled: pageStack.layers.depth < 2
+                onTriggered: pageStack.layers.push(devModePageComponent)
                 visible: Settings.developmentMode
             }
         ]
@@ -164,25 +170,17 @@ Kirigami.ApplicationWindow {
     }
     Component {
         id: settingsComponent
-        App.SettingsPage {
-            id: settingsPage
-            onIsCurrentPageChanged: settingsAction.enabled = !settingsPage.isCurrentPage
-        }
+        App.SettingsPage {}
     }
     Component {
         id: aboutComponent
-        App.AboutPage {
-            id: aboutPage
-            onIsCurrentPageChanged: aboutAction.enabled = !aboutPage.isCurrentPage
-        }
+        App.AboutPage {}
     }
     Component {
         id: statisticsComponent
         App.StatisticsPage {
-            id: statsPage
             reservationManager: ReservationManager
             tripGroupManager: TripGroupManager
-            onIsCurrentPageChanged: statsAction.enabled = !statsPage.isCurrentPage
         }
     }
         // replace loader with component once we depend on KHealthCertificate unconditionally