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 would If I were sure there is no .list in the code, but since it's not haml I can't search all the files for '.list', and searching for 'list' won't help as it's a common name. I'll think of a solution on a fresh mind tomorrow.