Keep IMBOutlineView from trying to expand inaccessible nodes while dragging accross such node's row

This particularly triggered opening access control views (like Facebook login) when dragging any object accross the item's row (NSOutlineView implements NSDraggingDestination and tries to expand any expandable node that is met while dragging).
Merge branch 'development' of github.com:iMediaSandboxing/iMedia into development