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.
I'd also include the `reboot one node at a time` recommendation from @jtuple docs. Otherwise, the user could end up with a cluster where all nodes must come back online to get quorum. For instance, in a system with `tree_trust=true`, and with `n=5`, if `3` nodes go down, when one comes back up the system is unavailable until the rest of the nodes come back online, since we still have a majority of untrusted trees.