Upgrade to recent Django version

assigned to @nnrcschmdt

First I will upgrade to 1.11.19, the most recent patch.

Afterwards I'm going to upgrade:

• 1.11.29 -> 2.0.0 (-> 2.0.13) -> 2.1.0 (-> 2.1.15) -> 2.2.0 -> 2.2.11

2.2 is also a LTS version and will have support until April 2022.

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mentioned in merge request !10 (merged)

closed via merge request !10 (merged)

mentioned in commit 8f28fd8d

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