Emiting flash message event on rootscope instead of context menu scope.

https://www.openproject.org/work_packages/9384

Perhaps someone wiser than me can tell me why the context menu controller scope has no parent scope. My fix is just to emit the event on rootscope but i get the feeling that if i understood ng-context-menu better there would be a way of correctly assigning the parent scope so the event would be picked up by rootscope as per usual.