expsose :leading_zeros to public API

As per current code drop down for day in f.datetime will never have leading_zeros. However the minutes will have leading_zeros.

The drop down value for day will not have leading_zeros and the 'false' is hardcoded there so no user option will do anything there.

However minutes part of datetime can be governed by user input.

I would say that :leading_zeros should be exposed to public API and year, month, day, hour, minute and seconds should obey :leading_zeros option passed by user. Right now some have hard coded value and some obey user input.

I am working on a patch.