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.
We are forcing a change through the installer, which is where
the majority starts from. We don't want to enforce a change
twice.
We can't really see if we installed or went through a factory
reset, so this is (was) the best of both worlds in conjunction
with the new installer feature.
While here, annotate that it is possible to leave it "empty".
This reverts commit 5eb2c986ca7233f0f94f372968433b145b4b3249.
