Provide before and after filter for java.util.Date

[tkurz]

Please add methods similar to

com.rbmhtechnology.searchlib.api.query.filter.Filter.after(String, ZonedDateTime)
com.rbmhtechnology.searchlib.api.query.filter.Filter.before(String, ZonedDateTime)
to be used with java.util.Date.

It would be easy to convert the Date to a ZonedDateTime outside the search lib. However, since it provides a Field Descriptor to handle java.util.Data (com.rbmhtechnology.searchlib.model.SingleValueFieldDescriptor.UtilDateFieldDescriptor) this conversion should be done by the search lib in that case to be sure the conversion is done in a consistent way.