Use clFinish to gurantee commands completed, instead of waiting for events.
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

no changes in code

The same code was repeated several time for different data types, so
it was extracted as a templated function to improve maintability and
make a code more clear.

Exception may be rasied inside the body of a copying constructor after
refcount has been increased, and beacause in the case of the exception
destrcutor is never called what causes memory leak. This commit adds a
workaround that calls the release() function before the exception is
thrown outside the contructor.

The entire AssetsLibrary framework is deprecated since iOS 8.0. The code
used in the camera example code can use UIKit to save videos to the
camera instead, which allows to avoid linking with PhotoKit instead to
prevent increasing the iOS deployment target.