Previously the search form on the /iqdb_queries page submitted directly
to the iqdb service (karasuma.donmai.us), which redirected back to
Danbooru with the search results.
This was different than API requests, which submitted to
/iqdb_queries.json which proxied the call to iqdb through Danbooru.
Because of this, searches on the /iqdb_queries page had different
behavior than API requests. Things like filesize limits and referrer
spoofing were handled differently.
Now searches on the /iqdb_queries page submit directly to Danbooru. This
is simpler and it means that API requests and HTML requests have the
same behavior.
* Change cutoffs on upload page to max 5 results, min. 20% similarity.
* Change cutoffs on standalone /iqdb_queries page to max 20 results, min. 0% similarity.
* /iqdb_queries.json: add `limit` and `similarity` params to change default cutoffs.
* Remove file_path_for, cropped_file_url (dead code)
* Remove complete_preview_file_url (preview_file_url now returns absolute links)
* Remove `file_name` (only used for Download link in sidebar)
