1.0.0 Release, Drop Django < 2 & Python 2 Support

Since the feature set hasn't changed for some time we decided to bump the version to 1.0.0.
With this release we drop the support for Django < 2 as well as Python 2.
The migration should be fairly simple since we only added a migration.
Test Envs have been updated.

Please do not install version 0.3.3. It will break you upgrade compatibility.

Have fun - feel free to contribute.
Thanks to @zypro for initiating the PR for the upgrade. We based the changes on #36