Ready: Strong consistency update

- [x] Configs in `advanced.config`
- [x] `riak-admin` interface for ensemble
- [x] Implementation details

Heads up to @andrewjstone, @engelsanchez, and @jtuple when he's back.
Maybe mention something in this section about how the vclocks for strong consistency differ from those for EC, but that they still appear as the opaque context.