resource scheduler: implement event propagation

[sanderr]

Since the scheduler does not receive / calculate increments, it needs to propagate events on the fly. When a task finishes, if resource.send_event=True AND there was an effective change, its dependencies can be added to the scheduled work. Implementation may need to acquire scheduler lock.

[sanderr]

assigning to Sander to check the events overview presentation for the current definition of event: is it just a deploy with change, or also any state change? In case of the latter, we have to be careful not to skip the dependencies (which is currently done in the handler but is proposed in the resource scheduler design to be done by the scheduler).