Manage our own "copy" action

[gbastien]

For now, using the classic "copy" action from Plone will give us the possibility to copy every existing object but our paste object just paste the items of our meetingGroup... We should not display the "copy" action on object not copyable... See if we can keep the classic Plone "copy" action and play with is condition (without changing it!) or add our own "copy" action...