We need it for support of autocompletion in admin pages.
* rename django.core.urlresolvers to django.urls
* update migrations
* fix warning about PercentagePerYearField.from_db_value() context arg
* fix warning about deprecated {% load staticfiles %}
This commit also remove support for py2.
* tox.ini: only run with py3
* remove all u'' strings
* remove imports from __future__