Beginnings of raft server and basic DB REST actions.

Summary:
Creates some basic REST endpoints for interacting with the db keyspace.
+ Lays the groundwork for raft consensus, though for this change it is not hooked up, yet.
+ Creates an extremely simple db (to be replaced by rocksdb) to use for now.

Test Plan: unit tests

Reviewers: strangemonad, spencerkimball

Reviewed By: spencerkimball

CC: team

Differential Revision: http://phabricator.andybons.com/D2