#315 - Extends NSOutlineView for proper handling mouse events

Iam referencing my Issue #315 from thursday, I have to fix this issue, cause I need it ;) It's something like "example solution", Iam new in Mono / Mono Mac / c#, but it works... I try to find mouse handler for List / TreeView but I was no able to find it... I have to extend NSOutlineView, like "Hywel Thomas" does it in "WidgetView".