WinRT/WinPhone: languages are missing from the generated manifest

Adding languages to the manifest in VS is a bit tedious. It needs to be done when packaging the app for the Windows Store, though it probably doesn't need to be done every time you generate the manifest (because Qt apps tend to put their translations in packaged files or QRC).

Similarly to capabilities and dependencies, the languages should be a list populated by a WINRT_MANIFEST variable. This can probably be auto-populated by the values in TRANSLATIONS.