[WIP][ticket/12649] Change sort & display options in footers to dropdown menu

https://tracker.phpbb.com/browse/PHPBB3-12649

![sort](https://cloud.githubusercontent.com/assets/3015760/3159613/b0ab4138-eb13-11e3-927b-f78bfc367f32.png)

Depends on: https://github.com/phpbb/phpbb/pull/2516 and https://github.com/phpbb/phpbb/pull/1864