[SERVICES] Merge ScmControlService() and ScmSendStartCommand() togeth…

…er (reactos#7392)

In addition:

- Acquire ControlServiceCriticalSection just before doing the pipe
  operations, and release it just after.

- SAL2-annotate ScmControlService().

- Re-order the ScmControlService() parameters in a more natural way
  (image comm pipe, service name, control code; then: arguments for
  the control command).

- Improve some DPRINTs.