Enable nice and ionice for Axii and all subprocesses via dedicated psutil API
This gets rid of the hardcoded nice ... ionice ...
in the build step.
We now depend on psutil which I also want to use for other things in the future (for example to get the 1m, 5m, 15m system load via API instead of parsing files)
Cleanup from !391 (closed)
Edited by Christian Dreher