stop using attr_accessible for sitewide setting model
Remove subsector name from title

It causes confusion because things can be repeated in the title and the
subsector name. Remove it from the title. It will still be in the
metadata so it isn't gone completely.
Merge pull request #1487 from alphagov/remove-sector-title

Remove subsector name from title
Merge pull request #1498 from alphagov/strong-params

stop using attr_accessible for sitewide setting model