Add native date/time dialogs on Android
This is largely building on top of Nico's work from KTrip and https://phabricator.kde.org/D29268. The native method registration issue mentioned there doesn't seem to occur anymore though, this works without any changes on the application side for Itinerary. The additional indirection using a library is needed so androiddeployqt does bundle the AAR file automatically.
On top of Nico's work this adds pre-selecting a date/time in the native dialogs and integrates this with the DateInput and TimeInput controls.