Use Shortcut for keyboard room switching

This allows to use the room switching shortcuts like Ctrl+PgUp/PgDn even
when the RoomPage doesn't currently have the focus. It's also a nice
code simplification.

src/qml/Page/RoomPage.qml

@@ -44,9 +44,6 @@ Kirigami.ScrollablePage {
         }
     }
 
-    signal switchRoomUp()
-    signal switchRoomDown()
-
     onCurrentRoomChanged: {
         applicationWindow().hoverLinkIndicator.text = "";
         messageListView.positionViewAtBeginning();
@@ -120,26 +117,8 @@ Kirigami.ScrollablePage {
 
     focus: true
 
-    Keys.onTabPressed: {
-        if (event.modifiers & Qt.ControlModifier) {
-            switchRoomDown();
-        }
-    }
-
-    Keys.onBacktabPressed: {
-        if (event.modifiers & Qt.ControlModifier) {
-            switchRoomUp();
-        }
-    }
-
     Keys.onPressed: {
-        if (event.key === Qt.Key_PageDown && (event.modifiers & Qt.ControlModifier)) {
-            event.accepted = true;
-            switchRoomDown();
-        } else if (event.key === Qt.Key_PageUp && (event.modifiers & Qt.ControlModifier)) {
-            event.accepted = true;
-            switchRoomUp();
-        } else if (!(event.modifiers & Qt.ControlModifier) && event.key < Qt.Key_Escape) {
+        if (!(event.modifiers & Qt.ControlModifier) && event.key < Qt.Key_Escape) {
             event.accepted = true;
             chatBox.chatBar.insertText(event.text);
             chatBox.chatBar.forceActiveFocus();

src/qml/main.qml

@@ -317,12 +317,16 @@ Kirigami.ApplicationWindow {
         RoomListPage {
             id: roomList
 
-            Connections {
-                target: root.roomPage
-                function onSwitchRoomUp() {
+            Shortcut {
+                sequences: ["Ctrl+PgUp", "Ctrl+Backtab"]
+                onActivated: {
                     roomList.goToPreviousRoom();
                 }
-                function onSwitchRoomDown() {
+            }
+
+            Shortcut {
+                sequences: ["Ctrl+PgDown", "Ctrl+Tab"]
+                onActivated: {
                     roomList.goToNextRoom();
                 }
             }