Only sortable columns will now have option to sort in UI.
Merge branch 'dev' into feature/column-sortation-tightening-up-9836
Removing currently selected sortable columns from lists in sorting modal.
Restrict selectable sorting options to those not selected yet


TODO: Add controller test
Add unit test for sorting modal
Add unit test for selectable sort option filtering
Merge branch 'feature/round-off-sorting-dialog-8280' into feature/column-sortation-tightening-up-9836
Add unit test for sort option filtering in sorting modal
Merge branch 'feature/column-sortation-tightening-up-9836' of github.com:opf/openproject into feature/column-sortation-tightening-up-9836

Conflicts:
	app/assets/javascripts/angular/controllers/dialogs/sorting.js
Include blank option in sorting dialog
Prune unselected sorting options
Prune sortingModal test case without assertions

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #1473 from opf/feature/round-off-sorting-dialog-8280

Feature/round off sorting dialog 8280