fix(README): use the new etcd-dev mailing list

We moved to google groups, update the URLs
fix(CONTRIBUTING): point to new mailing list
fix(peer join) fix wrong join command redirection
1. We use PUT request to do a V2 join. So we should redirect a PUT request rather than a POST.
2. /admin only accept V2Join request. Send out V2Join instead of V1Join.
Merge pull request #717 from xiangli-cmu/fix_join_redirection

fix(peer join) fix wrong join command redirection
docs(production-ready): explain the state of etcd clearly
Merge pull request #718 from bmizerany/master

docs(production-ready): explain the state of etcd clearly
feat(dashboard): add sigle-page-app html5 pushstate support
chore(dashboard): remove old dashboard
chore(dashboard): move dashboard server
feat(dashboard): project setup
feat(dashboard): key/value browser.
chore(stats): add vega depencency
feat(stats): stats page