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.
This sentence is a tautology ;) Additionally, reads are unavailable as part of the SC tradeoff as well. I would reword and expand upon it a bit. Here's a suggestion: 
```
When data is stored in a bucket with strong consistency guarantees, a
value is guaranteed readable by any client *immediately* after a
successful write has occurred to a given key. In this sense, Single-key
operations are atomic, and operations on a given key are linearizable. This
behavior comes at the expense of availability. The tradeoff is that a quorum of
primary vnodes for the portion of the keyspace containing the key included in
the client request must be online and reachable from the coordinating vnode of
the client request, or the request will fail.
```