cherry pick 6103e67e6141bb520060bb812ef0704cb96720cb python3 fixes
retain py2 compatibility
cherry pick https://github.com/artursmet/django-ajax-selects/commit/1e96a2eda73dc0366d08ccd58ee63912710973c3
Python 3 compatibility fix
cherry pick from https://github.com/artursmet/django-ajax-selects/commit/a6d8cc3ef1e12d5fc5e2cf5c28d6be95d08e6e06
@artursmet
Merge pull request
https://github.com/crucialfelix/django-ajax-selects/pull/72
python 3 support
Merge branch 'feature/python3' into develop