Initial report was mentioning the Classroom demo scene, but this is
probably because the scene was pre-configured to be used with OpenCL.
Would expect any OpenCL compositing to be failing prior to this fix.
The reason why crash was happening is due to OpenCL queue being
released from OpenCLDevice destructor. Is not that obvious, but
when Vector (including std::vector) is holding elements by value
a destructor will be called on "old" memory when vector capacitance
changes.
Solved by making forbidding copy semantic for compositor devices and
forcing move semantic to be used.
Also use emplace semantic in the devices vector initialization.
WorkPackages struct was created when scheduled. This patch keeps the
WorkPackages around and stores additional data with the workpackages.
The speedup is to small to notice, but it is needed as preparation
to introduce a faster scheduling method.
