Determine default sort order centrally

Currently, the default sort order of proposal dialogs is set in the proposal controller.
Instead, it should be set by the pager itself, since there are multiple ways to include pagers.
This prepares a common infrastructure for solr and database-based sorts.
Activate controversy sorting in Solr-based sorts

We overlooked this; controversy has only been activated for database-based pagers.
Fixes hhucn/adhocracy#299
Unify Solr/database sorting

Currently, the user profile setting of the default proposal sort order has no effect on database pagers.
Make database pagers and solr pagers share some of the same data sources.
Fixes hhucn/adhocracy.hhu_theme#298
Merge remote branch 'origin/develop' into develop