Make the Task type abstract
Closes #435 (closed)
Maybe you could check the performance on VIIA just to be sure. There should be no increase in memory consumption since we're still using a newtype for
Task and we remove events from strict data structures. There will be some performance penalty because we now check for each task application whether it concerns a
ServerInterruptedEvent. Previously this was only done in a few places, where it has been removed (see diff). This is intended; it was the main goal of centralizing task destruction. However it would be good to be sure the penalty is not too high.