mv_machine_learning: add multiple tasks support to MachineLearningNative module

mv_machine_learning: add multiple tasks support to MachineLearningNative module

[Issue type] : new feature

Add multiple tasks support to MachineLearningNative module. In case of
face recognition task group, two tasks - facenet and face_recognition -
are needed. Therefore, this patch adds a new API,
machine_learning_native_add() which adds a given task object to
the given context, to MachineLearningNative module, changes return type of
machine_learning_native_create() to void * type for API consistency, and
updates other task groups to call this API.

In addition, this patch drops a redundant parameter, task_name, from
machine_learning_native_destroy().

Change-Id: I9c3ca2645dc876a3c7eb31bb9ce0aca56d376ad9
Signed-off-by: Inki Dae <inki.dae@samsung.com>