Show ellipses for leaving rooms and space actions, and always confirm

The HIG suggests using ellipses for actions that have a confirmation,
and leaving a space or room is one such cases. Otherwise, the user has
no idea if leaving is an immediate, irreversible action.

It turns out there *was* some cases where pressing this button
(especially for spaces) would actually do it without confirmation, which
is now fixed.

src/spaces/SpaceHomePage.qml

@@ -95,9 +95,11 @@ ColumnLayout {
                     }
                 }
                 QQC2.Button {
-                    text: i18nc("@action:button", "Leave this space")
+                    text: i18nc("@action:button", "Leave this space…")
                     icon.name: "go-previous"
-                    onClicked: root.room.forget()
+                    onClicked: Qt.createComponent('org.kde.neochat', 'ConfirmLeaveDialog').createObject(root.QQC2.ApplicationWindow.window, {
+                        room: root.room
+                    }).open();
                 }
                 Item {
                     Layout.fillWidth: true