improve backend handling of duplicate issues
move duplicate issues into left list instead of separate tab
make issue status choices dependant on available outgoing workflow steps, implementing #2381,
also deprecating freelancing as a non-functional project setting, renaming functionality to allow setting status independantly of workflow
untablify attached files and links, also js-popupify link delete dialog
misc (very) minor bugfixes
make issue header scrolling fixer even smoother
improve attached image display in issue view