[bug 1100394] Implement simple_query_search in Advanced Search.

This was pretty easy. I still need to decide where the documentation should go. I kind of think it should be a KB article linked right from an (?)icon to the right of the search box.

Anyway, r?.

You probably shouldn't be using snowball here. This function will get used for non-localized fields, which means the standard analyzer will probably do a better job. For localized fields, [`es_query_with_analyzer`](https://github.com/mozilla/kitsune/blob/master/kitsune/search/es_utils.py#L829) will "upgrade" those fields to use the right analyzers. Since you're calling that, this should be fine.