Add multi-team support to this lovely script.

It's now possible to add multiple teams (there are none by default).

Instead of storing users as keys we're storing them as array items
instead because it didn't seem like there was any relevant information
stored in the user object (if a user isn't a team member anymore
what's the point of keeping their object around?).

We can now:
- list all teams
- create a team
- add a user to a team
- add oneself to a team
- remove a user from a team

Isn't it grand? Isn't it great?
Isn't it swell? Isn't it fun?
Isn't it?

Signed-off-by: Katie Delfin <katiedelfin@gmail.com>
Merge pull request #1 from olivierlacan/multi-teams

Add multi-team support to this lovely script.
Fix team removing logic for teams
Minor improvements to the team creation command

Also remove the keyword `new` from clearing a team as it might be confusing now that teams are created with a different command.
Refactor list teams command to show team sizes and empty teams list
Add support to remove/delete a team (admin user required)
Decorate team_name in messages
Add command header comments for better separation of the script
Support no 'team-name' specified for commands

Use a hidden default team label to store users that don't specify a team-name.
Update README with multi teams commands
Merge pull request #5 from hubot-scripts/multi-teams-followup

Multi teams followup
2.0.0