Added Service_GetStatus call

Added Service_GetStatus call returning in the SERVICE_STATUS property
status name (one of: Stopped, Starting, Stopping, Running, Resuming,
Pausing, Paused), or Absent when service does not exist. Target service
name is provided in the SERVICE_NAME property.
addressed issues mentioned in pull request
moved service state to string conversion to ServiceInstance class, accessible as GetServiceStateString(), + minor text changes