This commit looks horribly complex, but the main idea is to have each of the logic::commands
report their terminal OK state in the same way. That allow for leveraging this very moment
to initiate the idle timeout.
Additionally, I wanted to hide the logic of idle mode detection, which resulted in moving the
top level logic from main.cpp into logic/idle_mode.cpp and a set of additional files to compile
in unit tests.
D.R.racer