Starting on server-side validation.  Return an error message for
duplicate band names or duplicate artist names.
Data validation done.  This is all about duplication of values and
missing keys for creation.
More validation.  Don't allow people to do things they shouldn't be
allowed to do.  Sysadmin can do anything, baand admin can do
anything for a band, others can only do things that affect them
and no one else.