frontend, api: allow custom emails as commenters

I'm really sorry this came out as one huge commit, but I'm afraid
I can't split this up.

Closes https://gitlab.com/commento/commento-ce/issues/9

api/comment_new.go

@@ -116,5 +116,5 @@ func commentNewHandler(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	writeBody(w, response{"success": true, "commentHex": commentHex})
+	writeBody(w, response{"success": true, "commentHex": commentHex, "approved": state == "approved"})
 }