Switch back from 'sorting_order' to 'proposal_sort_order'
Compare https://github.com/hhucn/adhocracy.hhu_theme/issues/443
Change 'sorting_order' to 'proposal_sort_order' also in advanced user settings
Merge pull request #547 from MatthiasLittmann/fix_proposal_sort_order

Switch back from 'sorting_order' to 'proposal_sort_order'