Add Frontpage to Subreddit._specials.
PromoCampaign: add setters for location and priority.
edit_campaign: log location changes.
PromoCampaign: add target attribute.
PromoCampaign: dual write sr_names and target.
Add PromoCampaign.target backfill script.
PromoCampaign: use target instead of sr_name.
PromotedLink: don't cache_ignore embed attributes.
SubredditSelector: optionally include user's subscriptions.
PromoteLinkForm: suggest fewer subreddits.
Delete empty linkpromoteinfobar.html.
Use admin template AdminLinkInfoBar.
tdb_cassandra._by_fullname: Raise NotFound for single lookup.
VByName: except tdb_cassandra.NotFound.