Add option to not style input as readonly

[getup8]

That's it..

[getup8]

Current workaround (unless I'm missing something..) is to set attrs to anything valid, even if you don't want to add any attributes.

DateWidget(attrs={'data-readonly': 'false'})

Why this happens:
https://github.com/asaglimbeni/django-datetime-widget/blob/master/datetimewidget/widgets.py#L182

[symbiosdotwiki]

+1 for this

[C-BERBER]

This helped to open my text portion of the field but the X and the other button are still greyed out... Any thoughts? Thanks