Issue 171: Devided a basic part from ActorCollector

These patches mainly extract basic part for managing child processes from ActorCollector.
The newly extracted class is named ChildProcessManager. The motivation of it is to
manage new ArmPlugins that will be child processes by common code.

As a result, ActorCollector is in charge of tasks only for actions and became pared down.
In addition, A reset mechanism was reimplemented with signalfd (a specific feature of linux) to
wait for exit of a child. Since it is a kind of a file descriptor, it's easy to use in conjunction with GLib's
event loop.