***WIP*** First pass at range allocation. Lays down a basic algorithm for selecting a set of peers to send a new range to. MISSING 1) A lot of the config data structures are straw men right now 2) The actual data in the gossip 3) Most Tests

Test Plan: go test ./...

Reviewers: spencerkimball

Reviewed By: spencerkimball

Differential Revision: http://phabricator.andybons.com/D25