Bug 398505 - Rap: Context menus should be created only when needed 

https://bugs.eclipse.org/bugs/show_bug.cgi?id=398505

Partially reverted the last change because the menus should be available from the beginning and not only if a file gets selected (as in swing ui). This means lazy creation is not possible for the fileupload widget.
Also removed unnecessary code as already done in the other dropdown buttons.