Add support for Django 1.10, 1.11, 2.0, 2.1, drop support for Python 2

• fix #6 support Django 2
• fix #43 remove es_deactivate
• fix #44 add django 1.10 and 1.11 to test matrix
• fix #45 remove support for python 2
• In practice, Python 2 may work, but it is removed from the test matrix and won't be updated