Story 2096: Impliment Wagtail Integration

[jlchilders11]

Implement Wagtail Integrations:

Mixins

• FlaggedMixin - Adds a custom serve method to prevent unflagged users from seeing this page
• TaggableMixin - Adds the ability to tag pages for categorization

Routing

• RoutableHomePage - New home page for all wagtail interactions that allows for forwarding routing to child pages, e.g. if you get to wagtail through /outreach/, you will be routed through the OutreachHomePage

Posts

This is the bulk of the work, and is a porting of the existing Entry Model to Wagtail

• PostIndexPage - Index Page for Posts, implements most of the logic in formatting found in the news.views.EntryListView. NOTE: this uses queryparams for filtering the child pages, rather than seperate URLs
• PostPage - Functional translation of Entry, but uses a stream field rather than having separate models for different types of content. These can be filtered by the content of the stream field block

NOTES:

• Additional work/discussion is needed on the PollBlock. Currently this is not implemented, as it is disabled in the existing architecture, and will be non trivial to implement in Wagtail
• Additional work is needed for the video block to both automatically save the thumbnail, and display it instead of autoloading the video.

DEPLOYMENT NOTES:
When deploying this, a RoutableHomePage should be created and the existing OutreachHomePage should be moved under it to respect the new routing methods.

[gregjkal]

Per our conversation in standup: please test the homepage to make sure it won't break without manually migrating the existing testimonial and/or news items. If it does break, we need to either make these changes backwards-compatible (my strong preference!), with a follow-up change that cleans any bridge code up, or add a data migration so it can be fixed during the deploy instead of crashing until manual fixes.