systemctl: port to the new underline cell attribute

systemctl: port to the new underline cell attribute

And be more careful when adding color to log lines:

1. Apply color derived from load state only to load state (and in
   special cases to the circle at the beginning of the line)

2. Apply color derived from active/sub states only to active/sub states
   (and in special cases to the circle at the beginning of the line)

3. Special case the "exited" state of services, i.e. make the substate
   grey, as in this case the service is active, yet consumes no
   resources.

4. Cover the "inactive" state properly, by greying it our too

5. Downgrade the load state of "not-found" from red to yellow, since
   it's not really a case one needs to be come active on.