Change String length checks to .chars().len() instead of .len() because of UTF-8 characters

Currently, we check name (and likely other fields) length just with byte length (.len()), but to be e.g. able to properly validate arabic and other languages, we have to change it to `.chars().len()`

Also for city, city of birth, zip, identification etc. etc. where it makes sense

Also, it should be `.trim()`-ed for length