The test cases effectivly tested if the user_acl_check works which is already
covered by other test cases.

Prior to this change user passwords were not validated on change aside from
their length, but validated on login/bind by ldap3 with SASLprep. Instead of
using SASLprep on password change, this change restricts passwords to 7-bit
ASCII without control characters. Control characters are forbidden by
SASLprep. Multi-byte characters are uncommon in password, especially in those
generated by password managers. This ensures that passwords are always
SASLprep-safe without implementing the rather complex SASLprep algorithm. It
also allows us to fully describe the alphabet restrictions in the relevant
forms.

Fixes #100

Co-authored-by: psy <psy@darmstadt.ccc.de>

Add a few unit tests as well as integration tests that cover almost all views. Also fixed a lot of HTML validator errors.