Refactor and add some comments (ref #54)
Make sure object fields definitions are valid (ref #54)
Merge pull request #162 from spiral-project/54_add_object_field_type

Add object field type
First stone of list field type (ref #54)
Support subtype and subfields (ref #54)
List should just be a list of known itemtype (ref #54)
Test list of objects (fixes #54)