Add Extremem support for more diverse workloads

[kdnilsen]

As currently implemented, Extremem is best suited to modeling of application services that are running in steady state mode (allocating temporary objects at roughly the same pace they are discarding objects).

Extremem as currently impelmetned does not model workloads that depend on finalization or reference processing.

It also does not effectively model phase changes in which large numbers of newly allocated objects will have relatively long lifetimes (e.g. application startup and initialization) or in which large numbers of previously promoted objects are becoming garbage.

New workloads and configuration options for Extremem are required.