date_time_picker not respecting readonly/disabled flags

[toddhuish]

Connects to PR #490
I found a bug where class-acf-field-date_time_picker.php was missing some functionality that had been added at some time in the past to class-acf-field-date_picker.php which I was also expecting to work in date_time_picker. I've modified the code and created a PR for it.

[elliotcondon]

Thanks @toddhuish. Looks like we completely missed these attributes in the DateTimePicker class. I'll also take a look into the TimePicker class and will be sure to include this fix in the next release :)

[elliotcondon]

Update: I've manually added this missing logic to both the DateTimePicker and the TimePicket fields and will include in the next release :)