Include datetime.date in Datetime logical type inference

[tamargrey]

A featuretools issue from a while back (https://github.com/alteryx/featuretools/issues/150) noted a potential need for explicitly allowing datetime.date objects when checking whether something is datetime in nature.

Since then, Featuretools has started relying on Woodwork's type inference in determining whether data is datetime in nature. It may be useful if Woodwork's col_is_datetime included datetime.date in its checks.

We should determine what, if anything, adding a check for whether the data is a datetime.date to col_is_datetime adds to Woodwork's Datetime type inference.