Reduce number of events generated by step updates

[flosell]

Context & Problem

#135 pointed to an issue with the event-bus: All events go onto a single channel and only drop once all subscribers have processed it. Sometimes, these subscribers publish events themselves, adding more pressure to the event-bus.

We introduced a buffer to the event-bus to deal with a large number of events and reduced events sent by inheritance. But build steps are still able to send a huge number of events, jamming the event-bus.

Potential Solution

It's not necessary that every single intermediate update gets passed through the whole system; Instead, compress several writes to the results-channel into one update-event, similar to what we already did with inheritance or by throttling

[flosell]

Fixed, documented in wiki