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.
`some writes` -> `some operations`. 
`a node is unreachable` -> `if a majority of peers are unreachable.`