Split Feed model

[twm]

Much like Article in #415, the Feed model mixes server-set and client-set fields. Unlike that issue the primary concern here is lost updates.

Server-set fields

• url — may be updated
• next_check, last_checked, last_changed — timestamps
• error
• etag, last_modified, digest
• feed_title, site_url — feed metadata

Client-set fields

• url — entered by the user
• created, deleted
• user_title

Server- and client-set fields

• all_count
• unread_count
• fave_count

Proposed changes

Split into a few models:

Feed

Defines a feed to check. Contains the client-set fields.

The url field contains the URL originally entered by the user.

FeedState

Contains the server-set fields.

The current_url field contains the URL after persisting any permanent redirects.

FeedCounts

Contains all_count, unread_count, and fave_count. Maintained exclusively by triggers?