Exclude limit_choices_to attribute from field deconstruction for migration planning

[jeremystretch]

Proposed Changes

Extend our custom field deconstruction method to exclude a field's limit_choices_to attribute in addition to choices, help_text, and verbose_name (which are already excluded).

Justification

Changes to the limit_choices_to attribute on a field do not effect a database schema change. (In fact, we have many instances where the use of FeatureQuery() results in the dynamic calculation of acceptable values at runtime.) Excluding this attribute from consideration avoids creating "no-op" migrations which clutter the application.

[jeremystretch]

We can actually ignore related_name and related_query_name as well, and simply bypass RelatedField's deconstruct() method entirely. We'll need to do some extensive testing before implementing this change, however.