use notifications in InterruptController

[rottaran]

Otherwise the receiver cannot remember which interrupt was triggered. The old plan was to use an intermediate adapter from ISignalable to INotifier. Hoewever, this would be used almost always and we can eliminate the overhead.

Depends on #75 and #74.

The current implementation can be kept as an alternative and simplified tu use CapEntry instead of CapRef because the interrupt controller does not need to know about revoked reference capabilities.