Properly mark up the multi-app selector on editorial brand and operator shelf create/edit forms.
Merge pull request #20 from chuckharmston/multiselector-brands-opshelves

Properly mark up the multi-app selector on editorial brand and operator shelf create/edit forms.
Update preview when app is changed.
Merge pull request #18 from chuckharmston/update_preview

Update preview when app is changed.
Style the 'no apps' message in the multi-app selector.