Found using `codespell -q 3 --skip="*.po,./src/external" -I ../darktable-whitelist.txt`
where whitelist consisted of:
```
cas
childs
ect
eacg
isnt
liquify
nd
nonexistant
substract
thru
```
This PR is actually split up from #1576
.

(cherry picked from commit ca07fcc0)