Android: Detect is24Hour automatically if not specified

[philonor]

In Line 99, change [is24HourView](http://developer.android.com/reference/android/app/TimePickerDialog.html#TimePickerDialog%28android.content.Context, int, android.app.TimePickerDialog.OnTimeSetListener, int, int, boolean%29) argument value to:

• jsonDate.is24Hour only if it was specified explicitly (no false default value)
• otherwise DateFormat.is24HourFormat() reflecting system/locale setting