Add initial front end handling of question threads

@andy-armstrong, please review
Did this just get merged to master? Whatever you're doing here is breaking the translation infrastructure, you can't do these weird concatenations inside an ngettext phrase, it's getting very confused and returning this error:
```
Error: errors happened while running xgettext on discussion_thread_view_spec.js
./common/static/coffee/spec/discussion/view/discussion_thread_view_spec.js.c:201: warning: Empty msgid.  It is reserved by GNU gettext
```

What are you trying to display here? You need to do any logic before the ngettext, and simply pass the strings themselves directly into the ngettext call.