Organizer Configures Website Domain

[jonsgreen]

Organizer Configures Website Domain

Reason for Change

This PR will hopefully allow a url like railsconf.org/about to still route correctly to the latest railsconf site about page without having the event slug in the url.

Changes

• adds Website#domains field and DomainConstraint to allow for website matching without using slugs in the urls
• adds Website.domain_match for SQL matching of domains
• changes page_path route to have optional slug param so that navigation paths keep the slug out of url when using custom domain
• redirects to 404 page when website or page are not found

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[jonsgreen]

This PR was essentially merged though a later PR for landing page configuration that build on top of this one