Query: add offset option to jump to a specific row.
Store global defaults in LocalizedDefaultSubreddits.
Get defaults from LocalizedDefaultSubreddits instead of top_lang_srs.
inventory: Use LocalizedDefaultSubreddits instead of top_lang_srs.
Delete SubredditPopularityByLanguage.
Pick random subreddit using query offset.
Delete pop_reddits.
Delete usage of content_langs.
LocalizedDefaultSubreddits: remove subreddits in set_srs.

View._set_values only writes columns. To delete an existing column
we need to use View._remove.