Remove unused code
Make the query more tolerant of missing values


the filter mode deals with validation due to missing values
Add active model serialization to filter model
Serialize filters for query meta data returned by work packages API
Move setting of a default filter to client-side
Remove delay from filter editing when values are selected from drop down
Merge branch 'feature/angular-api-work-package-loading' of github.com:opf/openproject into feature/angular-api-work-package-loading