Added

Added a separate page for customizing a page type's categories and attributes.
- Reworked pretty much everywhere in the code to read from AttributeCategory/AttributeField/Attribute models instead of raw database rows on pages.
Added an extra call-to-action at the bottom of the dashboard for people who've activated premium but haven't activated any premium pages.
Added an "Appearance" default category to Landmarks with "Size", "Materials", and "Colors" prompts.
Added additional metadata for the code to consume for all AttributeFields.
Added links from the content customization page to customize individual page types, as well as the content#index pages.
Users can now preview premium pages without needing the permissions to create one.
Any custom field starting with the word "Private" is now treated as a private field.
Added name and universe_id caches on content models that pull from field changes.

Changed

Normalized the spacing between cards on the dashboard to make it look more even.
Returned the navbar to its original blue color.
Refactored the quick-add form to reuse field partials from the normal content forms.
Pages are no longer required to have a name upon creation. If they are not named, their name will appear as "Untitled" around the site, but still be blank in the form.
All existing text-based fields have transitioned into being custom attributes behind-the-scenes.
Field autocomplete is now per-label (instead of per-name) and has been enabled for all page types that match specific labels.
Instead of redirect :back, we now use Rails 5's redirect_back.
Tabbing through content fields no longer tabs to attribute dropdowns.

Fixed a bug that raised a 500 error after (successfully) creating a new custom attribute.
Fixed a bug that sometimes showed sidelinks on content to tabs that were entirely empty.
Fixed a bug keeping some edits from appearing in the changelog.
Fixed a bug preventing some contributor emails from sending.
Fixed broken header images around the site.