implement the ProcNode memory manager

[ichthyo]

Implement the actual low level memmory allocation used by render nodes and wiring descriptors, preferably by utilizing services of the backend.

The API and frontend of this memory manager, class AllocationCluster, is already in place and working, currently based on a dummy implementation of the actual allocation (which just uses C++ operator new for heap allocations). Thus this task is nicely separated from the rest of the implementation and could build upon the existing unit tests, which should be augmented for stress and performance testing.

[ichthyo]

and actually, this memory manager should in turn use the service of the mpool within the backend

[ichthyo]

future