control: Refactored control socket for registerable commands.
contol: move the control register command into the header file

Signed-off-by: Juhász Viktor <jviktor@balabit.hu>
control: rename the Commands to ControlCommand and some minor renaming are also made

Signed-off-by: Juhász Viktor <viktor.juhasz@balabit.com>
Merge pull request #336 from juhaszviktor/f/control_socket_refactor

F/control socket refactor