Stringoverrides

Makes everything in the world translatable via `admin/config/regional/stringoverrides`.

Here's the catch.  I can't save records here with the `$conf['locale_custom_strings_en']['']` setting in settings.php.  Removing it makes things work, but it means we have to manually add the string back in after deployment.  @sergii-tkachenko Anything I'm missing or does that seem right?

Also allows for easy Canadian translation to allow an admin use UI to fix #3545 and #3183.  

![screen shot 2014-11-25 at 5 37 32 pm](https://cloud.githubusercontent.com/assets/1236811/5193056/0dfc8b76-74cb-11e4-8f63-1ecf2ff2bdff.png)