Django 2.1 released

[dennissiemensma]

https://docs.djangoproject.com/en/2.1/releases/2.1/

[dennissiemensma]

Hmm, this also means support for Python 3.4 will end with this Django release.

"Django 2.1 supports Python 3.5, 3.6, and 3.7. Django 2.0 is the last version to support Python 3.4. We highly recommend and only officially support the latest release of each series."

And Python 3.4 will be supported until early next year, so at least six months.

"There are no specific plans for the next release of Python 3.4. However, the expectation is that Python 3.4.10 will be released in March of 2019, and this will be the final release of Python 3.4."

And I cannot support Python 3.7 yet, because the Dropbox client Pylama does not support it yet.

[dennissiemensma]

I've decided to drop support for Python 3.4. Even if there are users who cannot or do not want to upgrade, dsmr-reader v1.23 should suffice for most of their needs anyway. Until they're ready to upgrade some day.

[dennissiemensma]

Merged to development.

[dennissiemensma]

Reverted #512. Only requirements reverted, all other stuff is kept.

[dennissiemensma]

Will be released with #616. Direct upgrade to Django 2.2 if it works well.