Allow for a single hint and initially choose both date and time in DateTimePickerFields

[bundyo]

Currently the DateTimePickerFields has two distinct date and time fields which should be tapped separately to fill them up and have separate hints. It would be more logical to have a single hint property (even if empty) to cover both fields and on tap to allow filling them both with the combined iOS dialog and consecutive Android ones. Maybe optionally allow to fill both fields on every GridLayout tap.

Which platform(s) does your issue occur on?

• Both

Please, provide the following version numbers that your issue occurs with:

1.2.0