Fix description of voice control APIs

Fix description of voice control APIs

- Issue:
Some description for APIs does not explain exact behavior of each APIs.

- Solution:
This patch fixes the description of these APIs:
  - vc_set_invocation_name()
  - vc_set_server_dialog()
  - vc_unset_server_dialog()
  - vc_request_dialog()
  - vc_get_result()
  - vc_unset_result_cb()
  - vc_tts_set_utterance_status_cb()
  - vc_mgr_specific_engine_result_cb()
  - vc_mgr_get_current_commands()
  - vc_mgr_set_selected_results()
  - vc_mgr_set_all_result_cb()
  - vc_mgr_get_error_message()
The description of these APIs did not explain exact behavior of each
APIs.
And also, this patch fixes the order of retval to follow doxygen guide.

Change-Id: I4e1f0ab1db7cb4ecd7422315a7714f053aaf7d89
Signed-off-by: Suyeon Hwang <stom.hwang@samsung.com>