[smart_ptr] Rename to ivi::settings::unique_ptr.

[smart_ptr] Rename to ivi::settings::unique_ptr.

The name "smart_ptr" in the ivi::settings namespace does not
convey the actual semantics.  Rename to "unique_ptr" to better
reflect its C++11 std::unique_ptr<> style of behavior.

Change-Id: I0af30c6e3db88e08e0dcefe77206af1b3d4a255d
Signed-off-by: Ossama Othman <ossama.othman@intel.com>