Support concept of a group

[WesCossick]

A "group" would be a folder like a command, but without a .js file in it. It would still need a .json file though. It couldn't ever be run, of course, because there'd be no .js file to execute.

The help output would need to be clear that it was a group and not a command.

Errors would need to be presented for problematic designs (#7) related to groups. Some examples of bad JSON:

• Execute on cascade
• Accepts data