Fail noticeably when network things could not be started

[ahasselbring]

At the moment, the main network services (control message sender, status message receiver, team message receivers, monitor request receiver) are started in their own task and if something goes wrong (i.e. their port is already in use) they panic, but the user doesn't notice this. Therefore, initialization should happen outside of those tasks, i.e. start_network must fail.

Errors from start_runtime should probably be displayed in a graphical dialog in the launch handler.