feat(documentation): more documentation on app specific things

* Documentation of backend specific things
* Docuentation of the use of redux in the frontend
* Cleaned documentation elsewhere

Related to #74
9 jobs for master in 5 minutes and 59 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Check
passed #481747
docker
check_back

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passed #481748
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check_front

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  Test
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docker
test_back

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passed #481750
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test_frontend

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  Lint
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eslint

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passed #481751
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flake8

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  Svg Gen Docu
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generate_UML_svg

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  Documentation
passed #481754
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pages

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  Deploy
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