Wrap allianceauth.admin_status injection in try/except ImportError so
CI environments and non-AA projects don't blow up when allianceauth
is absent from the Python path.

Also updates README: fix 'mirgate' typo, add missing step 6 in Bare
Metal install, restructure Docker install steps (add migrate step,
separate media storage as optional step 5, fix a/b/c/d lettering,
fix 'Confimr' typo, correct step numbering throughout).