Adaptation for Django 1.10

[brawaga]

Without this patch I have no opportunity to build reports through many-to-many and reverse FKs.

[bufke]

Would you have time to contribute a unit test that passes in 1.9, fails in 1.10, but passes with this change? Unit tests are the best defense against regressions and keeping the code base maintainable with minimal time.

[brawaga]

@bufke, I understand, but I am short in time now.
Moreover, I am getting familiar with django report builder for a little time and do not feel confident for now.
BTW, if I become ready for that, could you provide a way to run tests for django report builder, I did not get this from any page of https://django-report-builder.readthedocs.io/en/latest/.

[bufke]

If I find any time I'll improve the docs on how unit tests should be written. The tests are just in one file here. You can run the demo app manually or by using docker - see the including docker-compose.yml file. Then just test with ./manage.py test as you would for any django project.

If someone can add unit tests here I'll merge it.

[bufke]

The utils issue was fixed. If there are other issues please open a new pull request with test. Changes that can break various django versions without a test proving which versions work will not be accepted.