Various small improvements to room filtering

Was originally #818

"Load more..." is still silly if you have a filter (potentially loading 100 rows that are all filtered out), but everything else should work.

![jabbr-new-lobby-filter](https://f.cloud.github.com/assets/1271535/389281/7ea743bc-a6fe-11e2-97dd-be0205e9dc84.png)