Add a few more i18n contexts

This should help resolve some of the issue in the de translation with
"Abfahrt" vs "Abflug", "abgebrochen" vs "storniert" vs "ausgefallen"
and "Termin" vs "Veranstaltung".

src/app/DepartureQueryPage.qml

@@ -40,7 +40,7 @@ Kirigami.ScrollablePage {
                     QQC2.Label {
                         text: {
                             if (departure.disruption == Disruption.NoService)
-                                return i18n("Cancelled");
+                                return i18nc("a train/bus journey cancelled by its operator", "Cancelled");
                             return (departure.departureDelay >= 0 ? "+" : "") + departure.departureDelay;
                         }
                         color: {
@@ -91,7 +91,7 @@ Kirigami.ScrollablePage {
                 // last row: arrival information
                 RowLayout {
                     QQC2.Label {
-                        text: i18n("To:")
+                        text: i18nc("destination", "To:")
                     }
                 }
                 RowLayout {

src/app/DetailsPage.qml

@@ -79,7 +79,7 @@ Kirigami.ScrollablePage {
         delegate: Component {
             Kirigami.Action {
                 text: {
-                    if (modelData.className == "CancelAction") return i18n("Cancel Reservation");
+                    if (modelData.className == "CancelAction") return i18nc("cancel as in revoking a booking", "Cancel Reservation");
                     if (modelData.className == "CheckInAction") return i18n("Check-in");
                     if (modelData.className == "DownloadAction") return i18n("Download");
                     if (modelData.className == "UpdateAction") return i18n("Change Reservation");

src/app/EventPage.qml

@@ -14,7 +14,7 @@ import "." as App
 
 App.DetailsPage {
     id: root
-    title: i18n("Event")
+    title: i18nc("event as in concert/conference/show, not as in appointment", "Event")
     editor: Component {
         App.EventEditor {
             batchId: root.batchId

src/app/FlightEditor.qml

@@ -71,11 +71,11 @@ App.EditorPage {
         QQC2.Label {
             Layout.columnSpan: 2
             Layout.fillWidth: true
-            text: i18n("Departure")
+            text: i18nc("flight departure", "Departure")
             horizontalAlignment: Qt.AlignHCenter
         }
         QQC2.Label {
-            text: i18n("Departure time:")
+            text: i18nc("flight departure time", "Departure time:")
         }
         App.DateTimeEdit {
             id: departureTime
@@ -83,14 +83,14 @@ App.EditorPage {
             propertyName: "departureTime"
         }
         QQC2.Label {
-            text: i18n("Departure terminal:")
+            text: i18nc("flight departure terminal", "Departure terminal:")
         }
         QQC2.TextField {
             id: departureTerminal
             text: reservation.reservationFor.departureTerminal
         }
         QQC2.Label {
-            text: i18n("Departure gate:")
+            text: i18nc("flight departure gate", "Departure gate:")
         }
         QQC2.TextField {
             id: departureGate