Update utils.py

add GenericForeignKey to InspectModel.relation_fields
Update utils.py
Update tests.py

added generic foreign key (and FK to contenttype) to ModeltoInspect and added test assertions for both; updated length of relation_fields.  Could have renamed/reused the FK to content type bc it's redundant with field "foreign" but wasn't sure if it's needed elsewhere.
Update tests.py

fixed typo
Update tests.py

add import for generic
added tests, updated test settings to include contenttypes
Merge branch 'patch'

Conflicts:
	inspect_model/tests.py
Merge branch 'master' of https://github.com/aschriner/django-inspect-model into aschriner-master

Conflicts:
	inspect_model/utils.py