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 realize this is a copy over mistake from @jtuple's doc. It also looks like it slipped by in the [code](https://github.com/basho/riak_ensemble/blob/develop/src/riak_ensemble_config.erl#L34). We can't have a default of `ensemble_tick * 2/3` because it will result in a `lease_duration` that is always smaller than `ensemble_tick`. I'm creating a PR to rectify that in the riak_ensemble code to default to `ensemble_tick*2` instead.