QML l10n fixes

- qsTr(): don't use + for visible strings.
- add welcomescreen to translation.pro

Change-Id: I361ef4a74bd0098cd7a7ee6b596b2b281661d50b
Reviewed-on: http://codereview.qt.nokia.com/920
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>

src/plugins/qmlprofiler/qml/TimeDisplay.qml

@@ -126,7 +126,7 @@ TiledCanvas {
             var timeDisplayBeginTime = Math.min(bt, et);
             var timeDisplayEndTime = Math.max(bt, et);
 
-            timeDisplayText.text = qsTr("length:")+detailedPrintTime(timeDisplayEndTime-timeDisplayBeginTime);
+            timeDisplayText.text = qsTr("length: %1").arg(detailedPrintTime(timeDisplayEndTime-timeDisplayBeginTime));
             timeDisplayEnd.visible = true;
             timeDisplayEnd.x = xpos + flick.x
         }