Allow users to manage select github teams

[patcon]

Not sure how we would want to do access-control here, but certain teams are a bit of a pain to manage through one person with admin access. Perhaps to start with, we create a whitelist of team names that can be managed via hubot.

Related: http://developer.github.com/v3/orgs/teams

cc: @emarchak (because an old email from you inspired this)