CP013: Introduce new properties and examples to affinity paper.

* Replace current motivational example with two new examples: one
showing migration of a pre-allocated container to gain affinity, and one
showing using the bulk_execution_affinity property to bind allocation
and execution locality.
* Introduce the `concurrency_t property`, reflecting that which was
previously available via the `execution_context`.
* Introduce the `execution_locality_intersection_t` property which
returns the maximum concurrency common to two executors.
* Introduce the `memory_locality_intersection_t` property which returns
true if two executors have a common address space.
* Make some other minor editorial fixes.

Author: Gordon Brown