Order rooms alphabetically preference

Defaults to order by user count
can change preference with /order or by using the drop down in the options menu
Changing ordering preference forces the Rooms room to update.

![options](https://cloud.githubusercontent.com/assets/7889474/3717014/c005fb52-161d-11e4-869c-eff4cb2cce50.jpg)

Well, this is probably wrong.

Do you really want the default `order` preference to be `{}`? It seems to me like `order` should be a string.