feat(settings): use configured site domain for undefined email addresses

Previously "localhost" was used as the default email domain.
Now the configured site domain is used instead.
3 jobs for ci-tests in 3 minutes and 56 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed #5854
make_deb_package

00:02:08

 
  Test
passed #5856
deb_package_test

00:01:46

failed #5855
make_test

00:02:23

 
Name Stage Failure
failed
make_test Test

----------------------------------------------------------------------
Ran 202 tests in 33.000s

FAILED (errors=20)
Destroying test database for alias 'default'...
make: *** [build/makefilet/include/python.mk:82: test-python] Error 1
Cleaning up file based variables
ERROR: Job failed: exit code 1