Fix broken links on various pages:
* The 'History' link in the sidebar on the post index page.
* The 'History' links on the tags index page.
* The 'Tag History' link in the sidebar on the wiki show page.
This will facilitate users being able to monitor tag changes from
a list of tags they are interested in. Currently, the only way to
do this is 2 separate queries on the added_tags and removed_tags.
- Tag matches allows a user to search for a single tag
-- Since testing for multiple tags would require converting the "tags"
string to an array which would most likely fail even for single tags
- Is new for quick searching of uploads or not uploads
* 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 ability to search /post_versions by added tags, removed tags, or
changed tags (added or removed).
* Add 'History' link to the sidebar of the /posts index. This is a
shortcut for a /post_versions search of the current tag.
