Support for nullable data types

[zfriedrich]

Hello, I noticed that nullable DateTime properties were not being copied in ObjectExtensions.GetDataReader. This change should add support for any properties of complex types that are nullables of a primitive type.

[ghost]

Thanks for this pull request, great idea. I've made a suggestion for a simplification when nullable types are used.

[ghost]

I'd suggest making a change more along the lines of:

.Select(p => new {
  name = p.Name,
  dataType = p.PropertyType,
  nullableDataType = NullablePrimativeType(p.PropertyType) != null,
})

In doing so the for loop later can be simplified:

foreach (var property in properties)
{
  var columnType = nullableDataType ?? property.PropertyType;
  var column = new DataColumn(property.name, columnType) 
  {
    AllowDBNull = nullableDataType != null
  }
  dataTable.Columns.Add(column);
}

Or something to that effect.