mv_machine_learning: introduce Context, ITask and adapter classes

mv_machine_learning: introduce Context, ITask and adapter classes

[Issue type] new feature

Introduced Context, ITask, and adapter class derived from ITask one.

With this patch, each Task API has a context which can have one more
itask objects for controlling inference or training modules.
The purpose of this patch is to keep same interfaces for each module.

As a reference, this patch applies this new approach to Face recognition
framework. This is just a step for next code refactoring
for multi models support.

Change-Id: Iad4c4df9fc87143723decadbc003787854e60e4b
Signed-off-by: Inki Dae <inki.dae@samsung.com>