It's the same as the implicitly defined one, and it causes a -Wextra warning
(not initializing the base class in a copy constructor).

This should allow many algorithms to take advantage of more parallelization
technologies.

This reverts commit fba72cb6, reversing
changes made to 02131ffb.

http://code.opencv.org/issues/2926

e.g. <opencv2/core/core.hpp> become <opencv2/core.hpp>

Also renamed <opencv2/core/opengl_interop.hpp> to <opencv2/core/opengl.hpp>

Made all STL usages explicit to be able automatically find all usages of
particular class or function.