wizard: remove "die" in favour of a graceful input validation / resubmit
wizard: remove "die" in favour of a graceful input validation / resubmit

Mostly prompted by the problem that mistyping the admin password
makes the form go boom.  We cannot rely on the browser.  While here
reformat and add copyright as various improvements have been made
here ever since 2015.

opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core,opnsense/core