poold: Move Logger class to logger.cc

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
poold: Move System class to system.cc

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
poold: Move Socket class to socket.cc

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
poold: Move Epoll class to epoll.cc

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
poold: Move SigHandler class to sighandler.cc

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>
cmake: Include new files to build process

Signed-off-by: Chrysostomos Nanakos <cnanakos@grnet.gr>