Add support for wildcard entries

[galargh]

It'd be cool if we could write something like: team.json:

{
  "team": {
    "*": {
      "permission": "push"
    }
  }
}

to give the team write permissions in all repos.

[galargh]

Or in YAML:

repositories:
  *:
    teams:
      push:
        - TEAM_NAME