Add support for cancelling enqueued inferences

If an enqueued inference is cancelled it is simply removed from the
queue.  Both a cancel inference response with status done and a
inference response with status cancelled are sent back.

Also override the new operators to call in the FreeRTOS allocator
instead of malloc/free.

Change-Id: I243e678aa6b996084c9b9be1d1b00ffcecc75bc9