Removed must-revalidate from aws headers
Fixed settings
Changed some `Contact` fields to be optional
Added wagtailsearch app, required when deleting a page
Fixed contact template
Fixed secondary menu

- Secondary menu doesn't show calling page if it has no children
Added `AliasPage`. Removed `MenuItem`

- `AliasPage` replaces `MenuItem`
- `AliasPage` allow a redirect to another page or url
- `AliasPage` is a wagtail `Page` and can be placed anywhere in the tree