stream-manager-dbus: Add new DBus methods to set/get volume rate

stream-manager-dbus: Add new DBus methods to set/get volume rate

  server          : org.pulseaudio.Server
  object path     : /org/pulseaudio/StreamManager
  interface       : org.pulseaudio.StreamManager

  method name     : SetVolumeRate
  method argument : string for direction ('in' or 'out')
                    unsigned int for stream index
                    double for rate (0.0 ~ 1.0)
  return value    : string for return message
                    - success          : "STREAM_MANAGER_RETURN_OK"
                    - no match found   : "STREAM_MANAGER_RETURN_ERROR_NO_STREAM"
                    - internal error   : "STREAM_MANAGER_RETURN_ERROR_INTERNAL"

  method name     : GetVolumeRate
  method argument : string for direction ('in' or 'out')
                    unsigned int for stream index
  return value    : double for rate (0.0 ~ 1.0)
                    string for return message
                    - success          : "STREAM_MANAGER_RETURN_OK"
                    - no match found   : "STREAM_MANAGER_RETURN_ERROR_NO_STREAM"

[Version] 11.1.40
[Issue type] New feature

Change-Id: I8a5b3ce87af5851c208df3a4ffa39ab6c8949a09
Signed-off-by: Sangchul Lee <sc11.lee@samsung.com>