fix keyboard shortcuts and help not working on workpackage list

[``* `#8747`keyboard shortcuts and help not working on workpackage list``](http://www.openproject.org/work_packages/8747)

@ulferts @myabc I decided to add another class for speed purposes instead of a data attribute ( I think it's faster than through some [data-list='true'] selector).
@ulferts I've introduced the list class to the list since the script was looking for a table.list. So if you think there are no more table.list on the project, I can remove the .list both from specs and the script