Allow only minDate or maxDate instead of requiring both

[chiester]

I think it should be possible to use only one of the [minDate, maxDate] attributes in datepicker. Suppose you had a requirement that no past dates were allowed, but any date in the future was allowed. You would only need to specify a minDate in that case. Currently if only a minDate is specified, it is ignored.

[javivelasco]

I think this is working in dev now!