FIX: Reset changed site settings after import is complete

After an import has finished the site settings should be reset to their
previous values. For example, since 'disable_emails' was set to false
before any import, it wasn't possible to login after the import
(sending email for password reset didn't work).
Merge pull request #2732 from gschlager/fix01

FIX: Reset changed site settings after import is complete