Restructure new CLI modules.

A few things have changed.  First of all, there is no separate copy of
the argparse-based `rqinfo` anymore.  It now fully utilizes the new
Click subcommand.  In other words: `rqinfo` and `rq info` both invoke
the same function under the hood.

In order to support this, the main command group now does NOT take
a `url` option and initializes the connection.  Besides supporting this
alias pattern, this change was useful for two more reasons: (1) it
allows us to add subcommands that don't need the Redis server running in
the future, and (2) it makes the `--url` option an option underneath
each subcommand.  This avoids command invocations that look like this:

    $ rq --url <url> info --more --flags

And instead allows us to pass the URL to each subcommand where it's
deemed necessary:

    $ rq info --url <url> --more --flags

Which is much friendlier to use/remember.