* Add search form above table.
* Move thumbnail to left of table when viewing history of single post.
* Remove unrelated links from subnav menu.
* Fix bugs with changed_tags search.
* Add thumbnails to /post_versions (when viewing history of a single
post, thumbnail is above table rather than in every table row).
* Combine user, date, and ip address columns into one column.
* Remove rating and parent columns (rating and parent changes are
already listed in the tags column).
@post_versions.empty? caused this query:
SELECT COUNT(count_column) FROM (SELECT 1 AS count_column FROM "post_versions" WHERE (true) LIMIT 20 OFFSET 0) subquery_for_count
which is unnecessary since @post_versions can be counted directly.
