Factor out hardcoded channels into slice of channels

  - Tie the series name, series columns to a slice index
  - Tie each series channel to slice index as well
Add consistent hashing support for clients

 - ChanGroup now has a name field, which is used as the key when hashing them
   Need to address how we name ChanGroups. Is it just target Hostname, which
   would make sense to me?
 - Modified groupcache/consistenthash to support returning *ChanGroup, and
   fixed up the tests
 - Need to figure out hash ring replication factor
Clean up Poster.delivery to noop on no points and up PostersPerHost
Merge pull request #1 from heroku/consistent-hashing

Consistent hashing