Fixes: #101 - Self referential object fields

[bctiemann]

Fixes: #101

Adds a LazyForeignKey class to handle self-referential single Object fields.

Adds circular import/recursion detection and skips object/multiobject field resolution on 2nd-level (related) object fields to avoid infinite loops.

Enables both single-object and multi-object self-referential field operation as shown below.

[bctiemann]

I had to reinstate the previous logic branch for cross-referential single object fields instead of using LazyForeignKey for both; strangely, with that change the UI functionality worked fine, but running the tests caused an error like ValueError: Cannot assign "<Table338Model: Second Object>": "Table337Model.related_object" must be a "Table338Model" instance. which was the reason for creating the LazyForeignKey in the first place.

I have yet to understand why the UI and the raw code work differently, and maybe it can be streamlined later, but for now at least both conditions work.