Re-organize the CLI commands by topic

The `amti` CLI has grown a number of commands (14 by my current count). Grouping the
commands hierarchically into several topics would present a friendly help interface to
users.

I'd tentatively suggest grouping the commands into `qualification`, `batch`, and `worker`
groups. If valuable, the new organization can be discussed further on this issue. Also, after
grouping the commands, it might be helpful to rename some of them to eliminate
redundancy. For example:

- `amti create-batch` to `amti batch create`
- `amti status-batch` to `amti batch status`
- `amti delete-batch` to `amti batch delete`
- etc.