mv_machine_leanring: code refactoring to face recognition

mv_machine_leanring: code refactoring to face recognition

[Issue type] : code refactoring

Did code refactoring to face recognition framework by doing,
	- Change feature vector file format to reduce unnecessary iteration
	  overhead.
	  [before]
	  |feature vector|one-hot-encoding-table|...|header|
	  [after]
	  [feature vector|label index|...|header|
	- Store data set to feature vector file after training because
	  we need to consider feature vector priority based data set
	  management policy later - this patch is just a step for it.
	- Several code cleanups.

On top of this patch, I will add the new data set management policy.

Change-Id: Ibaa866533a2f3187c353f6fb543821bb79ddfa98
Signed-off-by: Inki Dae <inki.dae@samsung.com>