Merge pull request #1345 from concourse/pr/github-team-name-and-slug

Add 'both' option to use team name AND slug in TeamNameField

This allows the connector to be configured with both so that both team names and slugs can be returned in the groups. This makes configuring teams in an application a bit more foolproof; we would often have confusion over whether the team name or slug should be given by the user, so it's easier to just allow both, since collisions shouldn't be possible anyway.