[bug 1018727] Backfill translations

This adds a "backfill translations" form to the admin allowing us to
backfill missing translations for responses. It's rough, but probably
good enough for now.

r?
Well shit:

```
u'sql': u"SELECT `feedback_response`.`id`, `feedback_response`.`prodchan`, `feedback_response`.`happy`, `feedback_response`.`url`, `feedback_response`.`description`, `feedback_response`.`translated_description`, `feedback_response`.`product`, `feedback_response`.`channel`, `feedback_response`.`version`, `feedback_response`.`locale`, `feedback_response`.`country`, `feedback_response`.`manufacturer`, `feedback_response`.`device`, `feedback_response`.`api`, `feedback_response`.`user_agent`, `feedback_response`.`browser`, `feedback_response`.`browser_version`, `feedback_response`.`platform`, `feedback_response`.`source`, `feedback_response`.`campaign`, `feedback_response`.`created` FROM `feedback_response` WHERE (`feedback_response`.`created` >= '2014-07-12 00:00:00'  AND `feedback_response`.`created` <= '2014-07-14 00:00:00' ) ORDER BY `feedback_response`.`created` DESC"
```

I thought doing `__lte` would pick up the entire day for date_end, but it don't. I'll fix that.

Good catch--thank you!