Support for [List] field

Added support for list fields.
Example usage within a viewer or other graph type:

[List]
public ListField<EntityA> EntityList => (context) =>
{
    return new List<EntityA>()
    {
        new EntityA { Id = new Guid(), Name = "No1" },
        new EntityA { Id = new Guid(), Name = "No2" }
    };
};

.NET Core projects support

Added support for .NET Core projects and added a build configuration for easy NuGet package building.

Initial repository transfer

This is the first published version.
All files were transfered from an internal repository at progresso group to github. Namespaces were changed to "Nitrolize".
Next steps:

• continue with code comments
• start documentation in wiki
• integrate helpers for Relay compatible Node field definition