Combine data-scroll-token and -contained-scroll-tokens

- Instead of using one attribute, use one that might just contain one token
 - Use the first token when tracking a child
 - Mandate that no commas can be in individual tokens

src/components/views/rooms/SearchResultTile.js

@@ -60,7 +60,7 @@ module.exports = React.createClass({
             }
         }
         return (
-            <li data-scroll-token={eventId+"+"+j}>
+            <li data-scroll-tokens={eventId+"+"+j}>
                 {ret}
             </li>);
     },