Forward traps as notification

[rottaran]

The ExecutionContext is informed about user-mode traps and cpu exceptions. Currently they are ignored and just suspend the execution context. In addition to the suspend, the trap should be delivered as notification to an INotifiable kernel object. The execution context cannot have nested traps, hence a single Notification instance is sufficient. The trap number and error are part of the thread state and can be read from there. The identifier in the notification is used by the trap handler to know which execution context trapped.

Depends on #75.